ive had a ashley full cat back system on mine for 2 weeks, big noticable difference threw the whole rev range, nice and raspy and didnt sound chav atall but was way stupidly loud

would have kept it if it was alot quiter
Edit:
Downsides were
*LOUD! perfect if you want a loud exhuast which dont down chav
*Mild steel so it will eventually rust
Upsides
*Sounded really nice
*looked good (twin 3" pipes)
*Noticeable power gains
*Price (£130ish brand new and can fit it yourself)