Too loud if you ask me. There are a couple of options though. Also there may be an underbike exhaust coming soon from a member on here.....
I personally have not gone for the tiny coke can exhaust, but will be getting a custom one made to suit the Jester seat unit, they aren't that much different in price than a good quality Arrow or something TBH.
As for what it does to your bike. Who knows? The Mivv cans are berated for bad running due to not enough back pressure and they are a full length can, not seen anyone complain about the shorty cans yet, you might need your fuelling adjusted slightly.