An high quality sports cat, like an HJS 200 cpsi, can cost from 500£ up to 800£. It has a 80% gas flow againts a 40-45% of a ceramic stock cat, that usually has a 500-800 cpsi density.
If you don't want to go decat (smell, MOT) it's the best choice, you'll get some increase, especially with a full exhaust and a good map.
It's very important that the cat has the right size, I've seen a lot of sports cats too small for the car which they were fitted to.
If the cats have too little noble metal on the matrix (that's the expensive part, Rhodium, Palladium and Platinum are not cheap!) it won't work.
So if you can't afford a good cat just go with a decat.
High quality sports cats have a lifespan of around 40-80k miles, depending on the driving style, if there's track use involved, weather etc... they decrease their catalytic capacity till the point they won't match the ECU values anymore and you'll get a CEL. The metal matrix shouldn't brake, that's a sign that the quality is bad, the metal is too thin or the position of the cat is wrong so the gas it's too hot or too concentrated in a single part of the matrix and has melt it.
On the RS3 we've seen that the car doesn't perform well with a complete decat (without a custom map, that is), the torque curve is much better leaving the 1st precat alone and fitting a sports cat.
The 172-182 is less sensible to back pressure and is much more permessive with emissions so spending 300-500 £ on a sports cat is not worth it unless you are very sensible to ecology and your standard cat is broken or you bought a car with a decat pipe (my case...I couldn't stand the smell and I had MOT coming, I found a used but still in good shape sports cat).
nothing wrong with standard cat tbh
