They're talking about actual HID retrofit kits, its a swapout of the bulb and the addition of the control ballast. Usually its pretty easy, but I've heard with 9007 there are issues with color and beam pattern, plus you loose the highs. Most people say "Well, you have HIDs you dont need highs" but on stock systems at least thats not the case. On my Lexus the stock HIDs have a leveling system which keeps the light level when the car is going up and down hills so they don't blind oncoming drivers. Well, the lights ae super bright, but there is a drastic cutoff right at the horizon line so when you're on a long dark road at night with no other cars you really need the highs.