Yep. You will have to re-fit the cat for the M.O.T.
Couldn't be bothered with that myself, but i managed to find a hi-flo cat off a 180 BHP golf4 anyway. It too had the 2 plugs for a lambda sensor. I just found a bolt big enough to fit it, and voila. No error codes. Working fine. Dunno how much difference the exhaust made performance wise, yet. Going in for the rolling road on sunday though. Should find out then. I had it rolling roaded just before the exhaust was fitted so it sould be a pretty true figure for power increase just from a full miltek system.
I just got my k03s aswell. But that aint getting fitted until after the rolling road. Then, straight after that its getting the retune with before and after figures. Once all thats complete, I'll be able to tell EXACTLY what I got for each component added. I'll post results here (well, I'll start a new post) once I'm finished it all, then everyone will be able to see what mods get what (for me at least, on a AGU), and can better decide what they would like to do. Don't expect it to be finished until January though. Gotta wait on my student loan for the remap...