Maybe, maybe not. The sellers of the expensive exhausts will of course be dumping on the cheap competition. Vishnu took a stock x-pipe and spend $100 on muffler shop crush bends to replace the cats and made great power, dyno tested. There should be a better quality control on the more expensive exhausts and there probably is. Whether it is necessary or not depends.
I ran ebay replica Supersprint headers for 2-3 years on my supercharged E36M3 and had no issues. I ran an ebay replica Supersprint rear exhaust for a year on my supercharged E36M3 and had no issues. After personally inspecting this ebay x-pipe from top to bottom, I am very impressed and have no immediate concerns about quality. I'll know more when I test fit it and when I cut it for the resonators. I want to see inside the x-section.
For those who need the name brand because they feel they have an expensive car that deserves only the best, there are already plenty of options. Give us low buck bang for the buck guys a break while we pursue our options. The guys who spend 3 times as much money may well get 2-3% more power and I think they should get a little more for their money. To me, the return on investment is poor.