Hi Ozzie. I've just had a powerflow cat back fitted at Brittania on siddals road in derby. They are the only ones without travelling for miles. They offered great advice - I only wanted a subtle note to the exhaust and they got it spot on. If you want loud they do loud! They go through all the different options with you. It was done in half a day. 240 quid all in, cannot fault them. Speak to the manager (older guy with a moustache) he knows his stuff. I went for a 3 1/2" tip with a muffler which is similar in size to the original, quiet when cruising, throaty when you press the loud pedal
Pic of my exhaust....