I've had a HID kit 6000K fitted to my 2002 166 2.0TS for over two years now, and it's passed two M.O.T.'s with no problems. The light output is much better than the ordinary bulbs that were fitted previously. Personally, I like the blueish colour of the 6000k bulbs, but you get most light output from 4300k, as someone mentioned earlier. I got a mate to fit mine as I am clueless about things like that, but it only took 30 or 40 minutes to fit both sides. We had to drill a hole through the plastic cover on the back of the headlights to pass the wires through, this is sealed with a rubber washer thingy, and the ballasts are cable tied nearby. I have never had a problem with them, I think I paid about £40 for them. I hardly ever use the main beam now.