I did this just this spring. I got a kit from HID country on ebay. Their ebay store was cheaper than their regular store.
I got the high/lo bulb and all it is, is just an electromagnet that moves the bulb. I really do not know if it makes a difference at night, I have yet to ride at night this summer, not sure how that has happened.
It is BRIGHT, like looking into the sun. I had to squash the wiring in the bucket to fit the bulb as it is longer than the h4 bulb is. The ballast and voltage unit are currently ziptied behind the bucket to the ears and hide out pretty good there. The relay is on the lower part of the neck. My ground is connected to my horn mount and + is on the battery. It has its own fuse too. My only gripe with the system is the connecter for the + wire is cheap and makes lousy connection so I replaced it and it is good.
Warms up in about 5 seconds from cold.
I have no idea how it is at night though. Our standard housings may not direct the beam very well but I dont know. Mine cost $50 for everything.
All in all, I like it. And if you dont, sell it and go back to h4 as you do not mod anything at all.
The ride IS the adventure. The destination is just to get gas!