I've never had an HID kit, though I have put H4s in a Miata before.
So, I don't really know what makes a good kit.
Of course, before you fork out the $$$$$ for a set, research, get to know what to look for, what you want, a vendores reputation, customer support, and any available into on the product you can. Also, remember that you are buying HEADLIGHTS! Those are something that NEEDS to be working properly for safe driving after dark or in bad weather (rain, fog, snow, or any other limited visibility conditions-> that serve to help YOU see, as well as for OTHER to see YOU).
Jeremy sells a good kit, from what I've heard. Others sell good ones too.
Get the one that works best for you, for the "right" price, and with the BEST customer service you can. Personally, I would rather pay a bit more and get someone that REALLY backs their sold products than get the cheapest available of a particular brand. Many sell and forget after the sale is done, leaving you to the manufacturer for anything in the future.
By reputation, Jeremy supports his products very well, is part of the community (so his people know what he is like and almost know him personally), and sells a higher end one. That counts for a good bit in my eyes.
Please do some searching!
Choose which "works" best for you . . .
Happy hunting!