Pro-Speed in Cardiff?
Only thing to worry about is the quality of the sports cat. Seen a number prove to be poor design and be quite restrictive, and others to fail MOTs 1-2 years down the line due to the poor quality catalyst. Other thing is the flange - I'm guessing they will want to chop the existing one off your current cat, rendering your original pipe useless.
Personally i would either buy an off the shelf de-cat, or buy a 3" flange online, and have a de-cat pipe mate that will mate with the rest of the exhaust, so you can swap it over.