I have been shooting my M2 since 2009. Its been a very good waterfowl gun and far more reliable than I would have expected from an auto loader. After doing some pattern work with factory loads and reloads, finding a choke I like, and installing a +25% recoil spring I couldn't be happier. The initial attraction of this gun was, like you stated, the balance and comfort when shouldering the firearm. I thought this was noticeably better than SBE2, Vinci, Berettas, Brownings, or even the Winchesters that I shouldered in the store or was lucky enough to try at the range. When it comes right down to it, the feel when it is in your hands is the key importance.
Oh, and that is even after I managed to flare the muzzle at the end of last season!