like he said.. I brought a HIDS4U kit for my 540i touring and it was perfect, so when I sold the car I decided to switch it over to the porsche. HIDS4U sent me some new bulbs and I just rigged it up. I found some flickering with the BMW, however the porsche has been spot on, and I think its mainly due to BMW fuses vs Porsche; I uprated both, but the BMW still blew fuses occasionally..
I got their new HIDS4U balasts with my kit (think it was called the pro kit or something) and they have been great; really fast warm-up, they flash perfectly (something the cheaper kits often fail to do) and they are very bright. They are 2yrs old now and still work perfectly, so Im well pleased..
HIDS4U are a bit more expensive than the competition, but Ill be honest; if I was buying another kit again today Id go back to them.. I had the wrong set of bulbs first time around for the BMW, and they sent out a new set straight away which were with me next day, plus helped me out with a wiring problem on the BM..
As for fitting, its easy enough, but give yourself plenty of time. Took me 40mins on the BM, probably 2hrs to do the first side and 45mins to do the other on the porsche. I mounted the balasts in the same place mentioned above, and didnt have too many problems with wire length or anything, my main issue was getting the wheelarch liner out on the near side (the screws were screwed! )
Well worth doing in my opinion, but I would buy the best kit I could justify; a mate brought a cheap kit from ebay for his lexarse and they are rubbish in comparison; I think my mrs 1-series with standard candle bulbs are more powerful. I rate my HID's a close second to my mates brand new SL with factory bi-xenon's
Ben