Re: Burris Fastfire red dot??
I don't use one for BE, but I have one on my M4gery and I find it to work very well. I like the way it automatically adjusts the brightness of the dot relative to the ambient light present. The sight is hardy and works great. Putting the cover on turns it off even if you've forgotten and left it on.
My first 100-yard group with the M4 after mounting the Fastfire was just over half an inch . . . I'm pleased enough with the thing that I think I'll simply buy another one instead of bothering to do research the next time I want an optic of this sort.