Nothing wrong with CAR irons. My 9mm AR, the one I shoot the most, has an A1 carry handle with an A2 aperture (my prefered rear sight). The better you shoot with irons, the better you'll shoot with an optic.
I prefer the dissipator set up though. If your bbl is .750 at the rifle FSB location, you can simply hack the front sight tower off (leave enough to act as a gas block though), touch up the bare metal with paint, K phos, or cold blue, and add another FSB in the rifle location. I've measured several M4 bbls that were .745-.750" where the FSB would land for a rifle sight radius. Seems like most were BMs, I wont swear to that though.
My 9mm is .718, so I'm going to have to get an A1 FSB and drill or ream it out. I'd have it done already but I keep forgetting to order the sight:banghead: Thankfully Kurt at KKF was willing to make a rimfire dissipator for me.