Here are some lessons distilled from my two-year experiment with the Fitsense FS-1 and one-week experience with the Garmin Forerunner 201.

The Fitsense and Garmin are based on entirely different premises, and therefore have entirely different strengths and weaknesses. The Fitsense works with moment-by-moment acceleration on the ground, through the mechanism of a food-pod accelerometer. When properly calibrated (and I'll talk about calibration in a moment), it can be very accurate. I've run 5 mile races and had it register 4.98 as I crossed the line. But its accuracy depends on many things: it varies with different terrain; with an increased or decreased stride rate (it implicitly encourages you to maintain a consistent stride rate; if you slow at the end of a race, it registers less distance); with uphills and downhills (it registers more distance and a faster pace going uphill; less distance and a slower pace going downhill); and with distance (if it's 2% short, for example, then it's obviously going to cut more mileage off a longer run). In large races where many people are wearing Fitsense and other wrist-devices, it goes haywire--or at least that's what it's done for me at the St. Jude Marathon for the past two years. (Other people's food-pod-to-wrist frequencies interfere with mine, apparently.) It does a great job on forest trails and in the vicinity of tall buildings, and of course it works great indoors. Properly calibrated, it gives you an almost immediate "current pace" reading; if I want to run 800s on a loop I've worked out in a local park, it stabilizes on current pace within a few seconds. There's no lag. On the other hand, the "current pace" it actually gives may oscillate 10-20 seconds a mile. Still, when you learn to work with it, it's pretty useful. If I want to run 800s in 3:00, I can look at the Fitsense and if it registers anywhere between 5:50 and 6:10--or if it bounces back and forth--I know I'm pretty much where I want to be. The "cumulative pace" reading is extremely useful in this context; after I've gone a couple of hundred yards, the cumulative pace reading is very accurate--although, of course, if the device is only 2% off, so that it reads 3:00 when I pass the half mile marker but the device itself reads .49, it's going to tell me that I ran a cumulative pace of 5:52 or so, rather than 6:00. I can live with that. For such short distances, I care about my measured loop, not the distance registered by Fitsense.

In races, properly calibrated, the Fitsense is, again, pretty accurate. But since it tends to register more distance--and thus a faster pace--at race paces (or perhaps at slightly increased "race stride-rates"), it may show me a cumulative pace that is 5 or 7 seconds a mile too fast. I may think that I'm right on a PR pace, then discover as I approach the finish line--if I haven't been paying attention to my actual time at each actual mile marker--that I'm lagging. What I actually do is use the cumulative pace as a general guide, but then make a point of hitting the "lap" button at each mile marker so I can go back after the race and find out what my splits actually were.

That's the Fitsense. It's a pretty good device. I calibrate the footpod by running a carefully-measured mile (measured with my accurate bike odometer) in a local park. If it reads too short of too long, I reduce or increase the CalVal a couple of points. That's at training pace. Prior to a race, I increase the CalVal a couple of points; that seems to work.

What about the Garmin?

Well, it CAN be extremely accurate, under certain circumstances. I first became aware of the device last September, when I was in the middle of the Tupelo 14.2 miler and realized that--perhaps because of the "increased stride rate during a race effect"--that my Fitsense was a full two-tenths of a mile off at the 7 mile point, and that my cumulative pace reading was, accordingly, about 20-25 seconds off. A guy I pulled even with was two HUNDREDTHS of a mile off. What was he wearing? A Forerunner 201. So I made a mental note to investigate the device. When I checked out this Amazon website, I found 150 posts about the Garmin and two about the Fitsense. The love-hate thing about the Garmin seemed to tilt noticeably towards the love, and the haters sometimes didn't seem to know how to optimize the unit. (I'm willing to believe that I haven't yet learned how to optimize it.)

The Garmin is clearly extremely accurate--more accurate than the Fitsense--on relatively flat or gently rolling courses that don't have much tree cover. I was astonished at how well it tracked with my bike odometer (without a single dropout) when I rode the Double Decker certified 10K course here in Oxford--EXCEPT for the miles in which the road narrowed and had tree cover, and/or went steeply uphill. Then it recorded less mileage.

When I ran on forest paths, however, its performance degraded severely.

The Garmin is not good--and clearly inferior to the Fitsense--in the matter of current pace, particularly quick response to current pace. When you start from a dead stop, current pace begins at 35:00/mile and slowly descends through 12:00, 11:00, down to whatever you're actually running. It takes at least 30 seconds, or maybe even 45 seconds, to register current pace accurately. So that for a particular application that's important to me--knowing what pace I'm running after the first hundred hards of a race and making small adjustments--it's distinctly inferior to the Fitsense.

Too, if you happen to pass under trees in the course of your run, the "current pace" begins to drop as signal is interrupted. This happens, I've noticed, even before the "low GPS signal" beeper chirps up. Then, when you come back out into the clear, the current pace reading sags in the other direction, to somewhat slower than you're actually running, as the device tosses all those missed hundredths of a mile (due to the momentary dropout) back into the averaged momentary pace. The phenomenon I'm talking about takes place when you set the device for "least smoothing." Of course if you set it for "more" or "most" smoothing, you notice none of this. That's because you've set your Forerunner up to be extremely unresponsive. When you set it on "most smoothing," the device is worse than useless for the sort of "repeat 800s on the road" interval work I describe above. Since ALL of its current pace readings are highly leveraged--actual current pace effectively averaged with current pace from 10 and 20 seconds ago; or rather, distance traveled in the last ten seconds averaged with distance traveled in the ten seconds before that--I want the least possible smoothing, which is to say the least possible moment-by-moment inaccuracy. This is especially true in race situations, where a momentary surge of 10-15 seconds a mile makes a huge difference in whether you're running the redline or over it.

One significant advantage of the Garmin over the Fitsense: on a flat open course, the Garmin is simply.....accurate. It doesn't need calibration. It doesn't gain or lose fractions of a mile if you slow your stride rate, or change surfaces. And as far as I can tell, it's unaffected by other nearby runners wearing wrist gizmos. So for a half marathon on country roads without tree cover--I'd go with the Garmin, if I had it, which I now do.

For forest trail runs, or for runs where I know I'm going to be dealing with tree cover or tall buildings, or for runs where my current pace is particularly important to me, I'm going to go back to the Fitsense.

There's more to say, obviously. Both devices are simply useful tools--and yes, as some have said, both can precipitate addictions! I'm continuing to experiment. I hope I've made clear that I'm willing to look honestly and the strengths and weaknesses of both devices, as I've discovered them. The Fitsense is fantastic--when it's not maddening (as it was for me at last year's St. Jude, where I simply abandoned all attempt at letting it register my mile pace (since it was registering 25% too short) and simply hit the log button at each mile marker, so I could do the postmortem with accurate splits.) From what I've seen, the Forerunner does a couple of things better and slightly more things not as well

The unit is great, but it's too finicky about picking up GPS signals.

While I'm running around Cambridge/Boston, MA, it NEVER picks up a signal.
Okay, maybe that's understandable in an urban area. But it doesn't pick up
a signal on the bridges between Cambridge and Boston, either. These are
long bridges, particularly the Harvard bridge, with no suspension
structure, nothing above the road except clear blue sky, but no GPS signal
picked up during the four minutes or so it takes to run across them.

Conversely, it picked up a signal just fine when I mistakenly left it
turned on while in my back-pack, in my house, in Woburn, MA, a suburban
area. Go figure.

How do car-mounted GPS units work in cities? Do they rely more upon the
car's known speed/direction to use dead-reckoning along the road? Or did
Garmin make compromises in the GPS signal handling in this unit to make it
fit on a wrist?

Other (minor) issues:

The manual is badly written. For every option, it explicitly spells out
the required button presses in painful details. The unit actually handles
menus very consistently: two buttons to scroll through the options; one
button to select the highlighted option (which may take you to a child
sub-menu); one button to back-out of a menu, to go to the parent menu. The
manual should have described this menu navigation scheme once, and then not
repeated it for every option, instead using the space to describe the
options in a little more detail.

The unit certainly knows the current date and time, as it's encoded in the
GPS signal, and it can be set to display the current time, but there's no
way to make it display the current date. That would have been useful.

It would be nice to turn off the GPS capabilities temporarily, for example
when you're in your basement den reviewing your past runs, and don't want
to be bothered by the warnings about a weak GPS signal.

I have ordered two Garmins now and tried to put them to use for my runs. The first unit I ordered locked up right out of the box. I returned it for a new one. The second one was highly problematic right out of the box. I upgraded the software for free on the Garmin website and it got much better. However, after miles of experimentation, I've decided that the Forerunner is not the right device for me. Really, it's because of the nature of GPS. Any time I hit heavier shade along my favorite path, the signal goes out. Smoothing helps me keep some of my assumed data, but I still lose more than I am comfortable with. Second, I do not like how inaccurate the pace measurement is. I don't even know why they have the main screen, the "real time" pace is so inaccurate it's completely useless. After way too many hours of online research, I finally found a way to get more accurate pace as I run. I had to set the custom screen for lap pace, average run pace and distance. I then set the autolap for .25 miles. So the average lap pace recalculated every .25 miles and was the most accurate of any reading I obtained to date. But I still worried that if I ever ran fartlke or tempo or did varying speed work of any kind, I'd never really know at the moment how fast I was running. That was very frustrating for me. However, it's the nature of this unit, it only checks your position every 10 seconds or so and if the satellite signal is weak while it's checking, your pace data is basically junk.

I'm sorry to return this item and sorry it isn't going to work for me. I have spent hours troubleshooting and now know more about GPS than I ever cared to! The features on the Forerunner are very cool, but I think for my money, I would have preferred less features and a stronger antennae!

Basically, if you like real time pace and you run in the shade (which really we should all be doing whenever possible!), this device isn't going to be nearly as accurate as advertised!

This device is great when it works. It frequently has difficulty picking up a signal (you must be at the top of a hill)and occasionally stops tracking/timing (reasons unknown). If you are walking or running in the woods or on a tree-lined street, forget it. Battery charging and life is excellent.

I have had my Forerunner for over a year now. What my experience has been:
1)Works better when battery is fully charged. After 2 hrs I lose signal strength to the point of the GPS not seeing part of my run.
2)It is not been very accurate . However, the unit was more reliable during the first couple months of owning it.
3)Do not try to use in wooded areas ,trees interfere with the signal to the satellites.
4)Battery efficiency drops off very fast after the 1st 6-10 charges.
Like most modern day gadgets needed to be perfected before releasing to the market.