I don't find it too loud to be socially acceptable, but quiet it isn't. It's still Euro/TUV/ABE/AFSF approved and comes with all the necessary paperwork. My butt tells me with this exhaust there is a bit more topend (it revs freeer), and maybe the bottom power has increased. My butt needs needs calibrating though, it has been a while.
I'd like to sum it like: the bike runs better, and without the catalytic converter you've lost the heat core under you left leg.