Cheap HID kits have flooded the market over the past decade bringing improved lighting to the masses at a fraction of the cost of OEM systems. Quality aftermarket kits used to cost around $500 not too long ago, now those prices have dropped dramatically. Why you may ask? Well think of it this way, what is the mother of invention?
The answer to that is necessity, and in this case a necessity to be able to compete and stay relevant when your competition builds and produces cheap systems for pennies on the dollar. Now there are cheap kits sold for exorbitant prices, brands that I shall refrain from mentioning for professional and legal reasons. Lets explore further.
The purpose of an HID system is to be an improvement on halogen/incandescent lighting. An HID bulbs is truly meant to be used in an HID projector, in order to avoid what will be a quite lengthy and technical explanation
of the purpose of an HID projector lets just say that it is meant to be used as control for the brighter light. We're talking about a system that at 35 watts is generally 3-5 times brighter than your average halogen bulb. Without a projector you end up with glare, glare that is dangerous to oncoming traffic and glare that just shoots out light all over the place, such as this image from pakwheels.com.
Adding in a quality HID projector completely transforms your output, you will have a much better spread, controlled output, a further reach, and on top of it all, you won't blind oncoming traffic! Now with that being said, the quality of the HID system matters as well, is it an AC kit, a DC kit? Is it true wattage measured at the ballast, at the bulb? What are its true lumen output? These are questions you need to consider.
Need to see a comparison? Checkout this video from the youtube channel 3slights.com, they show the light output differences between the quality Morimoto HID system and the cheap average eBay HID kit.
You saw the quality of the System matters, how about the bulbs? Well in this video by youtube channel fabolousg4ever, the user compares a set of cheap HID bulbs to Quality Morimoto bulbs in his factory OEM HID setup.