Mufflers that add sound and no performance aren't up my alley.
Is there any on the market that claim they add significant power or even noticable power?
the stock muffler mod can also be loud, but the way I do them is the added outlet is a series of 1/16ths holes on the bottom of the muffler right under the stock outlet. About 20 to 25 tiny holes and it lets out quite a bit of extra exhaust. It added a very small amount of 'extra noise" that can only be heard when the quad is nailed WOT. My quads are all efi machines so if I added too many holes, I'd have to get a new programmer.
With carbed quads, a dyno jet kit helps and you can really mod the stock muffler even more.
If the aftermarket exhaust mufflers claim that no jetting or a programmer is required, then IMO they really arent adding anything but sound.