I've been using a Fitbit over the past 15 months. It is an all-around excellent tool.
The Fitbit One is even better than the original fitbit ultra.
The only thing is you must be super vigilant with it. You can easily forget you have it on and if you
toss it in the washing machine, most likely you will have to replace it.
I've done this and loved it so much I've just bought another.
The Fitbit website is easy and fun, as well as the app.
I also own the Fitbit Aria scale which has been great as well.