The main complaint I have read about these types of watches is the strength of the vibration of the alarm. I bought this watch so I could wake up early without waking my wife. I am a very sound sleeper and have had no issues sleeping through the alarm. The watch itself has not caused any discomfort while sleeping.

My two complaints would be:
1) somewhat difficult navigation (but I think I have become spoiled by touch screen devices...), and
2) no snooze. I know it's bad to hit the snooze anyway, but I did sleep in once because of this