Fault wise have a look on here http://www.focusstoc.com/forums/topi...e-second-hand/

Mine made a few extra pops and bangs off a remap with Dreamscience but decating it made it happen loads more! If you go that route buy a lambda spacer so the warning light doesn't come on.
Exhaust wise personal preference I guess. I had a scorpion and it was very nice sounding. Not droning or very loud till you booted it.