I am reasonably happy with mine. It is louder than the standard system, but I can hardly hear it with the radio on around town. On the motorway, it is louder still and I have to turn the radio up, but then it would be and always has been. I checked underneath when I got home, they'd basically followed the original system but had the sense to move the middle expansion box further back - the one on my old system rattled against my gear linkages for months whilst I constantly adjusted and moved it around until I found a position where it didn't. I meant to tell the guys there about that problem but forgot and they seemed to figure it out for themselves. Really from what I've heard, it does depend on where you take it. I asked for a quiet exhaust and I think I got one.
Hmm. that is a bit worrying, although I have seen them come off cars before looking rather brown. I don't really know enough about this type of stainless steel to say whether a bit of rusting on the surface is a problem. I imagine it's just the chrome surface oxidising, but I dunno. If you've got your guarantee and you've taken it back to the dealer every year, you're entitled to a new one should it fail. That said, a warranty where you have to drive back to your powerflow dealer to get it checked every year is a bit annoying.
Chris.