If its just HIDs, they install just like regular bulbs and then you have to find a place to hide the ballast(s). Results are "meh", because HIDs are not designed to be used in reflector housings. Possibly brighter, probably actually, but the pattern is kind of poor.
If you have a glass fluted housing (one that you can't clearly see through) where the lens actually is what shapes the beam... it is 10 times worse.
If you mean the full on projector kit, they are a pain in the ass because you have to take the housing apart and modify it. But, that shit is like god's flashlight once its done.
The second option doesn't work with glass fluted lenses at all however.
Ebay has a kit for like $60 shipped.
I'm using it - comes with slim ballast and all wiring and bulb.
Simple plug and play.
Run the wire hanress, since it draws directly from the battery, mount the ballast, install the bulb and enjoy the 22nd century.