I can confirm that it's pretty good, but mine often loses track of time and needs to be calibrated via the app. I don't have it constantly connected to my phone, and only connect it ocasionally to sync, so maybe that could be the cause. I've even once had the calibration refuse to work, which required a hard reset of the watch to fix.

It's elegant, and the smartwatch features are unobtrusive, but I wouldn't trust it for any precise tracking, or even time tracking.