We use the Larue BUIS quite often on our rifle builds. It works very well when you combine it the Larue optic mounts that put the iron sights in the bottom third of the field of view. We find that most people that we have set up this combination for prefer it and state that they like this versus a flip-up rear sight as the iron sights are always there if they need them and are quickly transitioned to by tucking the chin down a little tighter. IMHO the Larue BUIS is simple and tough, it provides a simple sight that will give you the option of two different apertures. I prefer and recommend the same plane aperture for simplicity in most applications.
Here is one of our SLR15 Commanders set up with an Aimpoint
http://slr15.com/images/aarphotos/images/103_4345.jpg
http://slr15.com/images/aarphotos/images/103_4206.jpg
SLR15 Excalibur with the same set up
http://slr15.com/images/aarphotos/images/103_4191.jpg

