Hi. I've got a Scorpion round carbon fibre can fitted to mine with a removable baffle. This makes it street legal, but can be removed for track days if you want.
It sounds great and build quality is very good. Don't know about actual power gain, but a Scorpion can got the best result on a GSX1000R in a magazine test.
I used to have a Wolf oval can which was also good. Personally I prefer the look of the round can as it's quite chunky, which I think the Fazer needs. The oval looked a bit lost. Happy hunting.