I've got one on the AR I got from PBGUNRUNNER. You can get different modules for it to change how big the dot is. I think the smallest one is 1 MOA and the biggest one is 10 MOA if I'm not mistaken.
The things that stick out as being vulnerable to me is the diode module on top and the lack of protection for the glass which is covered by a small covering of plastic. They could probably beef it up a little by adding some rubber armor on there, and providing some kind of protective "hood" for the diode.
edit-Here is the one I have it's the tactical model with built on back up irons.
The only gripe I have with the BUIS is that the diode on top partially block the view though the arpurture (SP?) on the rear sight, You can work around it but it is kinda distracting at first.
I'll have to tell you on saturday. I'll be sighting it in on saturday after the range opens up for normall ops after we get done with the uspsa match.
The only thing I'm not sure of is how in the hell to adjust for windage. I see the up down screw on there but I see no l/r windage screw. There are screws on there that look like they MIGHT be it but I can't be sure becuase they aren't marked, and there is more than one screw on the side up by the sight glass.