I have found that the biggest mistake people make when mounting optics on AR's is that they mount them too far back and too low. The rear of the eyepiece for almost all optics mounted on AR rifles shouls be about where the rear sight would be. This one is mounted just about perfect.
I've been looking at the Vortex lines as well, I have a Vortex on my gopher gun right now and am very pleased with it! This little scope looks right on an AR and I'm looking forward to having one on one of mine!
Scott