They make a nice difference.
Fact! Thanks for the idea!
For everyone else, some real-world experience and thoughts -
I'm amazed how quiet it is with the DPs, 2.5" Thermal and Vibrant Ultra Quiets. I didn't dB test the before and after, but it's at least as quiet as with the exhaust only, and I'd swear it's a tad quieter.
I think this is a must-do for anyone that has an exhaust they feel is too loud, the Vibrants tame things WAY down. I was nervous that it would be too loud (for me) as a DD with the downpipes after reading a bunch of posts. I came out of a FBO Trackhawk with 3" Magnaflow and it literally rattled the stuff on the wall that abuts our garage when I'd warm it up in the Winter. It sounded Amazing, but made me self conscious at times. All my neighbors knew when I was leaving for work in the early morning, and I didn't want that again.