I have the BTG cat/back duals so here's my review.
First impression, well made, well engineered and easy to install. Straight-through flow design but expanded mesh in the muffler and resonators cause lots of air turbulence.
The sound at idle is a nice low rumble. On the highway at around 3000 to 4000 RPM an awful resonance would set in enough to loosen your fillings. I resolved to change out the muffler when I got around to it. The muffler is between the cat and the back axle in a straight section of pipe and could easily be changed.
After a couple of thousand miles, the resonance diminished quite a bit and became more tolerable as they broke in. A funny thing though, at one point when I damaged a wheel and was waiting for a new one, my local tire dealer loosened the flanges at the rear of the axle to get access to my spare tire and neglected to tighten them back. Well the exhaust system was much more quiet with the leak till I noticed the loose bolts. When I tightened them up again things got louder.
I give the system a passing grade but not a perfect score.
