1. legality
properly aimed headlights and colored lights will insure you won't get a real ticket
2 housing
cheap plastic usually is what melts, especially when you go from 35w to 55w hid's (why the 97-03 fogs sometimes melt)
now, a better quality housing, that was properly designed to dissipate heat and avoid uit at the same time will work fine. (most 00+ headlights)
3 plug n play
most hid's will work randomly when just thrown together w/ bulb connectors and thats it
so to fix a light oput or flickering you get a relay harness to supply the hids all the power they want straight from the battery w/o ****ing up the factory wiring. but because most vehicles were not designed for hid's there are bulb checkers that usually try and alert you to a bulb being out., so had to run resistors that matched the draw from a halogen bulb to reset the flickering lights and light out.
BI-XENON in factory housings w/o a retro
don't waste your money, all it is is a little magnet that pulls the bulb so it recreates a high beam spread. but w/o changing the intensity for the bulbs. they wll break and the bulbs cost the same as a single beam hid kit shipped,