I got a powerflow fitted earlier this year. I hear mixed reviews on them - I guess its like anything else really you wont know until you personally try it.

I must admit I'm very happy with mine. For the first week or so it was very loud and got me some funny looks. Although it then settled in and quietened down.

The benefit for me was that it was a good friend that does the powerflow exhaust at the garage I used so he obviously gave it a bit more care and attention.

I seem to see that a lot of people on this forum don't like powerflow though - But im happy.