The minis inherent reliability is very good, the real issue are the aftermarket magazines. I have a John masen 10rnd, the stock 5, and a tapco gen 1 30. The john masen and the stock work flawlessly, the tapco has major issues. Ive heard of issues with steel cased ammo, but from my experience mine has run it just fine. Wolf is a little on the weak side, and i swear it causes rust and crud to build up faster then any of the other rounds ive shot....it could just be me, but i only ran a couple hundred rounds thru my stainless mini about a week ago, and when i took it apart last night there was rust and crud all over the oprod, gastube, and barrel.
The mini is not really "Cleaner" then the AR, but it puts the crap in a different place, youll end up with a bunch of powder fouling around the op rod, gas tube, and in the forend of the stock. The AR will usually have a dirtier action, tho i call shins on AR DI systems being unreliable. Take a look over at perfectunion, they have probably the best group of mini fans around, lotsa good info. One thing to remember with the mini is its seriously over gassed, and uses a mechanical ejector, it will toss cases all over the place. Mine had, before i changed out the gas tube bushing, a nasty habit of finding the only bush nearby and tossing all my cases into it.