Seems like all the exhaust are overpriced for what they are.
I have heard the 2 Bros CF slipons and they sound great, deep mellow you know its a big bore bike.
The Yoshis look good and have a quieter sound at lower RPMs but really scream at higher RPMs.
Akra CF slipons have a little different sound all there own.
Price wise the Yoshis are about the least expensive of any that I looked at with the 2 Bros. in the middle and the Akras the most expensive at 1200 bucks list.
I never got the chance to look at Staintunes or Scorpion. You might try here http://www.hammythecanman.com