It's supposed to be motion activated, right? So once you've turned the sight on, do you ever actually have to manually turn the sight on again? From what I've read on Sig's site and a few reviews, it sounds like the sight just "sleeps" when you've parked it in a safe or wherever, and comes on again when it moves.
I believe Sig is only shipping the preinstalled dots as 3 MOA. In my experience with red dots, 6 MOA is far better for fast target acquisition, and especially in dim conditions a 3 MOA sight can be difficult to pick up sometimes.
I have a 3 MOA sight on my Walther PPS (Shield RMS-c) and wish the dot were larger. But other than that the sight has worked flawlessly.