I've had a set on my car for almost 2 years now. No problems with sealing, leaks, cracks, lag etc... They did give my exhaust note a different sound, no biggie there. I picked up some HP, I think it was about 16 HP at the higher end of the rpm band. My coating is still on there and I run hot EGT's (1600*+). No rust or bent flanges. Overall for $150 new I can't beat them. My OE headers had been welded SO many times they looked like they had some sort of disease! I would NOT put them on a motor that produces less than 450+ HP, they will do more hurt than good IMO.
HTH