It will change the sound of your exhaust...most claim that it will deepen your tone. Won't necessarily be louder, but will change the tone. Everyone I talked to felt it was a GOOD change. When I put one on my truck a couple years back, it sounded WAY different...just had a much more unique sound. But I also didn't feel it was actually LOUDER.
And I agree with Jerry above...as far as seeing any gains from it, when I installed the one on my truck, I honestly didn't notice any big gains on the "butt dyno"...I did see a very noticeable increase in gas mileage, but I also changed plugs, wires, dist. cap/rotor, O2 sensors, oil and gear oils all at the same time...so it could have been attributed to ANY of those things.