Yes they do work great, but with everything there are drawbacks. Expect to almost double your highspeed needle settings...the motor is gonna get alot more thirsty. Also, be VERY careful how much you tighten the muffler thru bolt...they snap very easily. I think I could open my own warehouse if I scoured the country for the backs of tower mufflers
Some people get rid of the stock thru bolt right off the bat and put a 6-32 threaded rod in it with a nylon locknut at either end. This works great, but again, even the 6-32 will snap from expansion if it's over tightened.