I just got the iPhone app and it seems to work great, have been ussing the Window 10 App and it (or the dongle) seems to have a problem in that often the Tracker is "No tFound" until I re-install the tracker and then it is found and Syncs
As to new App, I prefer the older Dashboard but that is a personal preference.
Resent iPhone user about Fitbit: Health & Fitness, v2.30