I think it made mine a bit louder back in the day. But if someone tells you it does anything else they deserve a kick to the bawlz because they sir, are phuggin liars.
It made my turbo louder. It was literally the first thing that gone done to my truck. But, now with a stereo system, straight piped exhaust, and a ****ered up fuel pressure gauge, I can barely hear it.
I believe the 03 ish turbos had the non removable rings without machining. So with that they are plenty loud for most anyone. Other than that there is no real benefit to this.