I have the fitbit One. Honestly I used it a lot for the first 4 months, then I stopped (it was Summer and frankly, I have no idea where to put the thing when I'm wearing a dress). It gave me a good idea of my activity level and how many steps my usual runs or errands are, but sometimes the numbers made no sense whatsoever so it was frustrating (like it said I burned more calories on a day when I had less steps and less 'intense minutes' than on another day with more of both). But yes, it was pretty useful to help figure out how active I really was.
I have a HRM (Polar) too, but I stopped using that a while ago too, although it's really useful to know how many calories you burn during your workouts (but it can double up with fitbit for runs etc so you have to take that into account). It's just kind of a pain at times, you have to put it on, sometimes it stops in the middle etc...
I'd love a bodymedia but the cost is turning me off, and I don't really want to have to wear that thing on my arm all day.