Ill not argue that each powerflow fitter is different but what i will also say is that powerflow offer fittings and customise everything where milltek etc all fail, they can make it as loud, quiet, free'er flowing, standard size etc, noone could do what i wanted except powerflow/blueflame type companies. I wanted a little increase in noise to compliment the induction noise up front. I knew that by adding a slightly larger diameter (2 1/6 to 2 1/4 inch upsize) I would probably get an increase in power anyway. Ive still got a stock downpipe and cat so there are still more gains to be had too! I cant comment for every powerflow franchise but I can seriously recommend them.