Kustom Kolors is a hobby paint by Valspar who makes HOK. It is not a 2k product.
Kustom Shop is just a relabeled production clear, they are not a manufacturer. They are owned by a distributor of many paint lines, TCP Global. The issue is you don't know exactly what it is, or warranty etc. You also are limited to their base coats etc... Not horrible stuff not great stuff, a few kustom painters have told me it's just PPG's bargain clear. However, they could make it whatever they want whenever. Unless you want to play jr chemist and mix paint lines, which is a really bad bad bad idea.
Higher solids content is part of it and a big deal when it comes to flow, clarity, durability etc...
Also HOK has a lot more UV protection built in.
Production clears vs kustom are different in how many mils of thickness they are built to take, strength and uv protection.
HOK is designed for thickness of up to 10x what a production clear will support, it has much stronger solvents to cross link specifically with their base coats and candies, sealers and primers. This is because with flakes and artwork etc. you will make a much thicker paint job than you would with a factory paint job. Part of why they are better for our application. Which is a custom application.
I took a HOK class where their tech guy. One of the other differences is that HOK tests like you wouldn't believe. UV baths, electron microscopes, etc... One of the main reasons I stick with them is tech support and knowing they will back me if there is an issue. I also feel that they have a much wider array of products than most other companies. I do use a lot of Autoair also.
PPG, Dupont, Basf are also good choices but I can't get them in small quantities, unreduced, and affordable like I can from Coast Airbrush.