Passed the MOT ("Hauptuntersuchung") with the wrapped catalyst. My assessment: if you don't run the car (and its catalyst) on a track, you will probably not reach a sufficient temperature in the catalyst for it to work properly. I therefore recommend wrapping it for "normal" road use. However, at the beginning of the test, the not so hot catalyst "produced" CO2 that was through the roof. It took a few rev-ups until they came down sufficiently. The engine idle was still not perfect, but better than before - and it passed the test.
