They are quiet and cheap,but way to restrictive.I had a Summit split rear system on my 98 Ram and just the other day had to replace the muffler(turbo).I bought one of their "race" mufflers to replace it (flowmaster copy).I am already seeing pretty good gains in fuel milage.Based on that,the turbo must have been a big kink in the system.If you look inside it,you can see why.
Oh,but it is way louder!