One of my pet subjects, this......
There's a thread on here about the reconditioning of my OEM cats, by a German company, using metal substrate cats that are better than OEM quality. Cost to refurb 2 was less than one OEM cat (when they were available),but it is a bit of a mission to do.
http://forum.a8parts.co.uk/showthrea...ight=converter
The vast majority of low end replacement cats are designed to have a life of x2 MOTs - the one it just failed that's forcing you to replace the cats, plus the next one to scrape through, so the warranty on the cat has expired before what little precious metal has actually stuck to the poorly made substrate from India has gone astray. This assumes the washcoat was actually up to spec in the first place, and that the company that made it did proper 'worst case' testing amongst the 500-odd models the cat itself can be canned to work on.....
The only exception to this is German 'Blauer Engel' parts, which you'll struggle to get in the UK as the market favours the £200 options over the near-OEM level parts.
The issue with 'sports cats' is that they're usually a low cell count in order to make them more free flowing. They could work, if only they made them with sufficient wash coat to counter the more free flowing nature. They do a job, but basically the dodge ref spacing out the lambda sensors is so the probe isn't 'sniffing' as instantaneously as the ECU would like, so it then misses the spikes in emissions that the cats can't deal with.
The UN regs need re-writing to make aftermarket products closer in quality to OEM, but for the moment the race is to the bottom in terms of price and therefore quality....