Over the past 2-3 months it seems to have become fashionable for aftermarket exhausts to be 'dissed', The std exhaust costs 50% more than even the cheapest aftermarket system, has only 12mths warranty and sounds s**te, it also weighs about 7kg more than an afternarket one, I looked at mine when it came off and it's very poorly made imo
It's not like your ever going to get upto 20bhp extra like you can get on a scooby or evo so imo it just comes down to a budget, noise and look of the tailpipes, surely difference between a £300 and a £600 is 1-2bhp at best on a N/A engine thats already pushing out a decent output to start with