My first try-out for the Garmin was Ironman Arizona, and it worked spectacularly well there. I got it right before the race and never tried it anywhere else before. IM Arizona is in Tempe, AZ, and the bike course goes out in the desert from Tempe. Great exposure to the Southern skies as they say.
There was one minor glitch. Although the Garmin was new, it barely lasted for the duration of my ride. And I am pretty fast on the bike. By the time I rolled in it was already giving me warnings of a low battery. In subsequent races I would learn not to turn it on until after the swim. Unfortunately, that just adds another layer of complexity.
What I found next was not so good. Here in Berkeley, with all its wooded hills and narrow canyons, the Garmin did not perform nearly as well. Half the time, I ended up in the scenery or cutting out entire swaths of road. The worst was the altimeter. When the unit can't find a good signal, it switches to a built-in barometer and then altitude jumps of 3-500 ft are not uncommon. Parts of my rides looked so jittery you would think there was a major quake.
All those extras add up rather quickly and I often found my rides inflated by 10 or more miles, and the climbing by and extra 3-6,000 ft. I guess that is what beginning riders love!
Next came the download issue. I am an avid Mac user and refuse to buy a windows box or use one of the windows boxes my wife has. Garmin's website, motionbased kept having trouble with my Macintosh. They did fix some of it over time, but never quite enough to remove all the headaches. And then they delete all but the last 10 of your downloads unless you pay them a monthly fee. Go figure ! Why would I want to pay someone a retainer just to access my old data? And why do I need to be online to look at my data? It is a hassle really.
In short, the Garmin was just an endless array of little nuisance factors and in the end, I had enough and tried to sell it on eBay. But before that could go through, my teenage son picked it up for its "gadget appeal."
So here we are, several years later. My son still uses the Garmin from time to time. The glitches are better but many are still there. The tracking is much better and he hardly ever goes off road like I used to. The altitude is better too. But I suspect it is because motionbased corrects the data. They keep him on the road by using maps. That looks good but it is cheating. And what is the point of GPS if you end up using a map anyways? How can you trust the values that way?
The device works best in open country, no hills to speak of, no trees, and certainly no narrow canyons. You better make sure it is fully charged before every ride and even then it won't last for a whole century, unless you plan to ride without stopping. The lap feature works but more often than not it just causes errors. The interface needs a lot of work and it is something only PC users can love.
Downloading is still a pain. They resolved the Mac issues but it takes forever. You have to wait to get your data, and sometimes you have to wait a long time. I can download all the data from my Ergomo (onto my computer by the way!) and get all the info I need before motionbased gets around to start "processing" the Garmin runs.
You can keep rides on the device but the more rides you keep the slower the downloads go. Each time you download and process you move another one of your old rides out of reach (you only get to keep 10). I can keep hundreds of rides from my Ergomo on my computer for free. And I can access them anywhere, and anytime. I can get to the original raw data, as well as the processed data. And my Ergomo's battery is good for a week at least.
In short, I think the GPS is a bad deal. You get lousy battery life, a so-so user interface (really needs some Steve Jobs here), a painstakingly slow download that can take hours, a very limited history (unless you want to keep paying them), a subset of features (unless you want to struggle with microsoft or read manuals or both), and worst of all, "massaged data" that you have no control over. The latter is by far the worst problem and one that should give you pause if nothing else.
The positives are that you can see where you went. That is great if you happen to suffer from Alzheimer's disease, but I never have trouble remembering where I went. If you rely on the GPS though, you will never find your way again without it.
The trouble with GPS and other route-finding software is that it dumbs you down. You come to rely on it and then you can't remember how you got there. Like speed dial numbers. You friend is number 3, and that is all you remember. Come to a new phone and you are lost. The same applies to GPS. When the device runs out of juice or breaks, it leaves you stranded like a little kid in a foreign city. I know so many people with GPS in their cars, who can't find their local grocery store anymore. I think it is better to stay aware while you are alive. That way you get to enjoy it more.
As for training, the value is extremely limited. It is cool to fly over your route and get all that video-game entertainment, but most of that is a waste of time really. Better get on your bike and ride a bit more.
On the other hand, if you are in it to impress your friends with cool gadgets, it might be something to consider;) Better to impress them with your riding though! More difficult perhaps but far more enjoyable in the end.