Ive got the Ktec sports cat on mine and it passed its MOT no problems. It’ll be going in for it’s second MOT with it on next month, so I’ll keep you posted.
I’ve only done around 3000 miles in the car with it fitted but no issues so far. I’ll admit that I’m thinking about swapping back to a decat after it gets another years ticket on it so I can save the Ktec cat for MOT’s. There’s a rattle starting to happen under my car though and it’s either my center pipe of the exhaust going (I hope) or the cat is starting to fall apart. I’ve gone under the car and whacked it a few times and can’t seem to hear it mind you.
Mine still triggers the EML light every now and then but that may be down to the absolute shite home brew map the previous owner had on it.
As long as you’re not doing mega mileage, you’ll be fine. Unless you’re willing to pay the silly prices OEM cats go for these days, it either an eBay special or a more expensive Magnaflow/Ktec sports cat.