My HM has the 2-1 system, and my wife's HM has the 2-2 slip-ons, so...
The 2-2 doesn't seem to offer much more performance than stock. However, it definitely sounds great with the dB killers removed. I don't find it all that loud, but if you do, you can always wear earplugs (which you should on any bike anyway, due to wind noise if nothing else).
My 2-1 system is definitely faster than stock, and a tad louder (actually sharper sound) than the 2-2.
I will admit that most onlookers, almost to a person, prefer the way her bike looks with the twin cans. (Part of that may be the fact that her stock carbon side covers remain in place, while mine had to be replaced with ugly plastic ones...)
Both systems offer considerable weight loss - from the bike, as well as the wallet...
