I have one. It sits on a rifle with a Comp M4 (not the S like yours) in a LaRue flip to side mount (I also highly recommend the LaRue mount).
It works great, is very clear, and while it isn't cheap at all, it is definitely high quality. It doesn't make the Aimpoint the equal of a good telescopic sight or ACOG, but it can help you use it not only as a fantastic CQB optic but also something that's capable of decent precision at longer ranges. Still not quite what I'd choose for under-MOA precision, but for minute of bad guy or for hunting, it is quite good.