My experience with yellowing epoxy so far is that West Systems is worse than MAS epoxy. I think it's an aging thing with the hardener, but not sure. They are both easy to use. One trick I'll pass along is once you've coated your board with epoxy, take a hair dryer or heat gun and gently warm the coating. This will release the air bubbles that get entrained in the epoxy during mixing and also make the coat flow out more evenly. Don't overheat, just a gentle pass....you'll be amazed...