I think they sound great. Just a tad loud but that's OK.  Only one problem that I have had is rust.

 

The black paint on them is just a finish paint and not worth beans.  I painted the mufflers with a high temp paint inside and out and this helps a lot.  You need to keep an eye on the chrome tips. they need to be kept clean of rust too.

 

The sound is a deep growl at idle and seems smooth at speed.   I have a video on youtube, search for kbd corvette muffler sound.  I have a crappy camera but you get the point.

 

I give it an 8-9 for sound and performance,  a 5 for finish since I had to paint them.