I bought this watch just to have a silent alarm clock so I could get up at 4:30 without waking my wife -- for that it works great.  Some reviews indicate that it isn't strong enough -- the vibration seems a little light, but has never failed to wake me.  If I have a flight or a meeting I absolutely can't be late for, I still set a backup alarm, but have never had to use it.

It is comfortable enough to sleep with -- at first it was awkward having something on my wrist, but I think it took a couple of days before I didn't even notice I was wearing it.  Not the best looking watch, but very functional.