I'm using a Nikon 1-4 x 20 M-223 with the Nikon non adjustable mount.
This is on a Colt LE6920 that still has the front sight post. No problems at all. The front sight post is visible but transparent at the same time enough that I can see through it and never notice it.
I'm not a fan of red dots that take a battery for obvious reasons. Speed wise I feel a scope that is 1x loses nothing. Plus the option of 4x for a more precise 100+ yard shot if needed is still there.