me and phil had this 'quarrel' a year or so back and I was saying my Cupra had a decat and no problems whatsoever...
However, after about 9 months with it fitted, the pre lambda sensor was shot and lights started appearing. A lambda sensor is extremely expensive, so together with the cost of the decat, its way more expensive than just doing the sensible thing from the start; buy a sports cat from one of the known brands, blue flame, supersprint etc
yes phil you were right...man enough to admit