I have sports cats (200 cell powerflow systems) on both my Moon VT6 and the Scottie. Both had standard turbos (with staggered seals) until recently when the Scottie went Stage 3 - prior to that the Scottie ran perfectly well for two years, and the original turbo is still running fine in another member's car as far as I know. The Moon is still standard, and again I have had no turbo issues.
You just need half a tank of petrol to get through an MOT, as the emissions test can still be tricky

, but you don't need the hassle of swapping exhausts at MOT time when decatted.