I bought a competing product, the Bodymedia Fit, last September.
I've lost over twenty pounds since I began using the device. Their advertising says it's like "having a personal trainer on your arm." I figured that was over-the-top marketing BS but there's more than a grain of truth to it. When I get lazy and don't feel like hitting my daily walking goal, for example, I think about having to sync my armband with the website and "fessing up" that I hadn't exercised. It makes me get off my dead butt.