My tti, 3" with the Super Flo mufflers, is way quieter than my crap exhaust before it. I can carry on a conversation without yelling to the person next to me. Stomp the loud pedal and it gets louder, but it's quiet enough, I think its too quiet sometimes.
My complaints with my kit are:
1) I had to shave a nut down to fit in the bend on the the first pipe after the headers. I think if you go 2.5" you won't have a problem.
2) The second pipe, the one with the cross-over, came squished in the packaging and the opening at the front was squared, not round. Both sides somewhat, but the drivers was worse, had to pull it out quite a bit. Channel locks and problem fixed.
3) For my 66 the tail pipes were (are) a little long, maybe 3-4". The tips go on just before the bumper and stick out past the bumper. A fusie should be just fine.
I agree with Commando that universal mounts aren't the best. I would have preferred a different option for the tail pipes, but as my car had nothing, they were all good.
Other than that little list of issues, I love the tti exhaust. I think it sounds great, isn't loud when I don't want it to be and I did it myself with basic tools.