I'm happy to report that my 2+ year old Moto Droid Razr works well with the vivofit and Garmin Connect Mobile. I had to root & upgrade to Android KitKat before it would work, and it took some "fiddling" to get the vivofit to sync. But after the initial pairing was done, the vivofit has been syncing flawlessly with the phone.
I tried with Android 4.3, but GC immediately reported that my phone was not compatible. 4.4 solved that.
I'm running CyanogenMod 11, for what it's worth. Not bad for what was probably one of the first BLE / Bluetooth Smart Android phones on the market.