Not to be inquisitive, but I wonder how they make money. From the website it seems they only sell Fitbit . Amazing how one such stream of income can support the whole enterprise and generate revenue.
This model (free service/soft + hardware) reminds me of sports-tracker.com  (one of few sites I simply love). They service (app, site) is also free and they sell heart rate monitors.
With same model (do free service, sell hardware), there is one difference which is interesting. Sports-Tracker sells their own hardware, MyFitnessPal just resells Fitbit.