After watching videos and reading reviews about their 350Z exhaust I must say it appears to be very impressive. The Y pipe going into a resonance chamber looks kinda korny to me. I always prefer the dual. But, if it works, don't question it.
Heres a review of the ART pipes and their TDX vs "Brand X" where they prove the "myth".
Nissan 350Z Motordyne ART Products - Fact Or Fiction - Import Tuner Magazine