The only real negatives I've heard about the B&B systems is the resonance. Kinda notorious for it. Other than that, nice system w/ great sound. I did read somewhere that the newer designed B&B systems for C4's have been modified to reduce resonance...the old 3" systems were supposedly kinda tough to live with.
I, for one, love a healthy sounding exhaust (I'm running LT headers w/ no cats and Maganaflow mufflers - sounds mean) but interior resonance is something else entirely. Auto trans cars can even be worse. I'm lucky w/ my system as resonance is minimal at best but if I were in your shoes and looking at a B&B system, I'd prefer to hear one 1st in a C4 before buying.
Jeff