i use to have an m3 2002 and i installed hid kit on it. I bought the cheapest kit on ebay cause i was thinking that all of the hid kit on the market is the same. It was the biggest mistake of my life. The bad quality hid kit runed my fuse box and i had to change it..... i did regret not to buy a good quality hid kit. I now own a 328i 2010, same as you and i didnt bought the car with xenon. The car came stock with Halogen. I did some crazy research and i found out that for germans cars, the best hid conversion kit is the canbus ballast 55w. So i bought mine on the net for 139.99 usd shipping included. its been almost 1 year and no problem at all. No flickering and no error on the dash. The website where i bought it from is www.xenonhidconversionkit.com
. Im thinking now of converting also my fog lights. All this was to say that its maybe better to add a little bit of buks but at the end its worthed.