ive got a powerflow on mine......only bought it because it was the nearest, cheapest option for me at the time as my standard exhaust had blown into oblivion. ive had it on my car now for about 18 months, had it checked and my certificate stamped etc etc and there have been no issues for me.
Im led to believe that the quality WILL differ from fitter to fitter but thats the risk you'll have to take.