Comfortable, waterproof (I always wear in shower), measurements seem pretty accurate mostly (though I have a low HR and looks to me like it usually doubles HRs under 40 as often happens to me on my phone app). I have a Huawei phone & sync's well - in initial days seemed to need to reconnect band & phone a lot but increasingly stable). GPS display of workout in app is great and other data input & display pretty user-friendly but not clear that there is a way to download data or chart in app itself (e.g. resting HR every day). Easy to customise which apps notify via vibrate - great way not to miss phone calls (but equally to know that someone's ringing if put phone itself on silent). Runs for quite a while after charging even with 1hr GPS use most days. Does sometimes start workout itself for no apparent reason (perhaps button pressed by accident - sometimes with water pressure in shower, sometimes when in bed) which drains battery if you don't catch it (once woke with no battery life as apparently gone for a 90 minute workout in my sleep...). Strap does come loose sometimes but band never fallen off as doesn't easily come out of main loop through.
Edit Nov18: watch itself still going great but strap leaves a lot to be desired - increasingly loose on clasp (though still not outright fallen off, just frequently goes loose on wrist, quite a few times a day) and one half came away from watch front fixing - I managed to cobble back together with super glue and a tiny screw and still wearing daily a few months on but not impressed. Looks like they've responded to criticisms and made Band 3 strap a normal watch fastening and with replaceable bands, so will probably look to purchase that whenever this one becomes unusable