I ummed and arred about fitting a SS Exhaust on my car. Could only find powerflow at the time and although it was slightly cheaper than the genuine BMW one all reviews of people who had had it fitted were poor so i got a genuine BMW one for about £540 which included new mounting brackets and rubbers. About 1 week after i bought that one and had it fitted i found Fritz. They seem to really know what they are doing and i have my car booked in with them to have a big brake conversion done.

I think your decision should depend on whether you want an original car or if you don't mind having non original parts. If it was me i would definantly buy the SS system including the manifold. The original manifold is very restrictive and you will gain a considerable increase in power for that alone. Matched with the SS back box and you will probable gain about 10-15% more power or about 20-25bhp.  When i have the money i will be buying the Manifold, but that will come after i have had the seats retrimmed.