Let me throw you another curve...check out the SureFire M73 too!
I own (or have owned) a KAC, a M73, Troy MRF and hopefully a LaRue next week
All are a quality products that do their jobs very, very well. I've handled C4iGrants LaRue enough to determine that it is the best bang for the buck, period. That said, if installation is not your thing or if you don't feel like sending your upper off to someone that can I would suggest the M73 or the Troy MRF. The M73 is very simple, pop off your hold handguard, pop on the M73 and tighten down two set screws. The Troy requires you to cut off your Delta ring and the snap ring so you'll need a dremel tool. The Troy is a little on the heavy side. It's not a bad heavy; it is heavier than the M73, LaRue and KAC but not as heavy as a SIR.
HTH