What does the fitbit log for you?
Is the fact that you have it on your wrist a motivator to getting it done? For example I tried using just an app but I became uninterested, sometimes forgot and so on.
In essence it logs steps, and calculates calories burnt from that, you add water drunk, specific workouts, food, and it works out whether you're gonna gain or lose weight and how fast. It also tracks sleep but I don't really see the point of that.