When I did mine it was plug and play, although the kit I bought had larger ballasts (cigarette packet size) so I had to drill the back of the light covers to run the cables through with a grommet for weather proofing. Probably took me an hour but then I hadn't done it before, and I also managed to lose the little spring clip that holds the bulbs in place, so had to make one up by bending a paperclip to replace it.
No canbus errors, they just worked. I went for 35W 4300K, so they look like OEM ones in terms of colour, the car sailed through the MOT with no comments at all. Much, much better than the standard halogen lights.