SO FAR SO GOOD..
Ive had good luck after I contacted polar to fix the no syncing issue. Please see "wont sync.. Check this fix.!!!"
I have discovered that the app needs to be open when you sync to it. Also you you need to sync a few times a day.. No big deal for really.. Dont let the plethora of bad reviews about not syncing detour your decision to get the app. I had the same issues but they are fixable... BTY. Polar responded very quickly with the fix.. Im totally happy with the M400 and the Flow app..
CRFpilot about
Polar Flow, v3.1