I've heard one - and it has a nice sound, but like any aftermarket Boxster exhaust that has two individual, seperate mufflers, it will drone like a sumb1tch between 2,000 and 3,500 RPM. It is so loud that you can't hold a conversation in the car. I like loud exhausts and I positively cannot tolerate it.
Incidentally, I built a borla "clone" using magnaflow muffers. Pics of it are here:
http://vorlon.case.edu/~jpv/boxexhaust/
It would be great for a track car or a deaf person. Sounds great everywhere (really, really great) but just drones too much for me. I built it to be light, and it is (10lbs total).
John V