Supersprint is probably one of the nicest sounding systems out there, but for the price, nowhere near worth it.
Go for a custom build, can tweak it to your specifications (how you want it to sound & look) and will cost you considerably less than a 'branded' exhaust. Neither one will really make a difference to performance, not on a car with such little power anyway. A custom cat-back system shouldn't cost you more than £350 fitted - just make sure you find a reputable exhaust place