My personal opinion is steer well clear, from the day i had mine fitted in redhill surrey i had continuous problems, as was previously stated alot depends on the fitter, but
My personal experience is:
The steel goes yellow in no time at all
The resonace of the exhaust inside the car is unbelievable and can give you a headache on long journeys
The quality of the fitting was questionable,
rattles and clunks from underneath
Addition of a second silencer made very little difference to the noise, but did roll off the performance a bit
The exhaust tone changes dramatically once the car is warm and also gets
way louder, (this thing would turn the heads of TVR drivers beleive me)
I then had it removed by JKM portsmouth and had a supersprint fitted, although i noticed a slight performance decrease i was
far happier with the product, quiet under normal driving and then it bursts into life when you open the throttle.
My girlfriend has a powerflow on her
Ibiza GTI and its good with none of my problems, but in my honest opinion its not worth the risk,