You are kidding ? Powerflow are some of the most aborted cock ups of systems i have ever had the misfortune of witnessing. Most of them are put together by people who can barely weld let alone have any comprehension of a motor car or what an exhaust is for. How many of you have looked at the mess they make and actually know what you are looking for/at ? All the ones i have seen have been M.I.G. welded and very poorly too. I doubt if they even know how to operate a T.I.G. welder which is the best machine for welding Stainless Steel with, however, when you advertise that your product is Stainless and don't quite declare that it is the lowest grade of Stainless Steel allowable to be branded as such, you can get away with using a M.I.G.
Do yourself a favour, either buy one which has been made for your car and proven to at least NOT decrease power or find a specialist who will make one to your requirements. You may pay a little extra for a genuinely good system but it's better than wasting good money on a Stevie Wonder special.