Don't think there's much comparison tbh.. The Nismo and fujitsubo exhaust are very similar but you won't find a new one of those on eBay for the price of a pair of trainers.
It's horses for courses, personally I prefer buying brand named stuff always have. Im the same with clothes, I just like it that way.
Exhaust may be fine, if I needed to replace an exhaust because I was selling the car I would probably risk it.... Besides eBay brings me a lot of business, I get a good proportion of custom from people that buy cheap crap off eBay and find out it doesn't fit or breaks after a few months. (Buy cheap buy twice) is a very true slogan in my experience.
Personally I would save up and get some thing you can be proud of but each to their own as they say.
I killed my scorpion with heat Too much heat buckled the internal baffles or something, the exhaust stained. I sent it back and they opened it up, found it non repairable and sent a new one out. I then traded it for a buddyclub with a member on here
Scorpion have been a pleasure to deal with and would always recommend their exhausts
To be fair the ebay dudes will also do an exchange if their model breaks too..............you'll get 5 magnetic fuel savers and an electric supercharger instead.