Isn't the downpipe and cat one piece on millktek's and aftermarket's?
For another £100 i'd just get a sports cat. No need to take it off once a year, no risk in getting caught, no EML light, no smells, backfires or anything else!
Also decat's make it loud as fook!
JMO but I couldn't be doing with the hasstle and expense of swapping over all the time !
Sam