My Powerflow was fine on my old cab and I had no issues at all with the quality of the pipes and yes the fitting and the welds are dependant on the person doing it that's for sure. If anyone wants to go custom then I personally recommend these lads in Sheffield
http://www.exhaustsuk.co.uk/ as they did the system on my Rallye and it's sound, you just need to look past the fast and furious website ! There's also a firm called pipe werks in Lancashire that are not cheap but are knocking out quality systems and their website is here
http://www.pipewerx.com/ I can't personally recommend these but from I'm seen on other forums I've never seen anyone say anything negative about them.