The only optic I have (that's worth a damn
)
EOTech 512 mounted directly to the flattop rail. I don't have a BUIS yet because when I get my Sabre Defence barrel tomorrow, the EOTech is going on that Mid-Length build.
I'll most likely go with an ARMS #40, but I don't know if I'll get a riser for the EOTech or not. I would like it to sit above the FSB a little more, but I have no problems shooting with it right now.
I got the EOthingy because I liked the 1MOA dot in the center. More precise (IMHO, of course) for the longer shots (400, 500, 600, and 700yds) that I play around with when the corn and beans are down around here in the Fall, Winter, and early Spring. This is all with the appropriate Kentucky Elevation, of course. I thought the 4MOA dot of the Aimpoint was going to cover too much real-estate at the longer ranges, so that was a big reason I didn't go that route.
Pile on top of that that the EOTech is made in the
USA, was cheaper because I didn't need to buy an expensive mount, and it came in a model with VERY common batteries (AA) so the choice was easy for me.
That's what I bought, how I mount it, and why I bought it. Hope this helps.
WIZZO