Welcome to the forum.
If I were in the market to buy products for an epoxy floor, I would buy them from a vendor on this forum. I am not saying the Costco epoxy product isn't any good, it may be just fine. However, the vendors here on this forum have excellent products and they stand behind those products and they have excellent customer service. If you have an issue, they can, and they will, help you. I am not knocking Costco products or their customer service, I shop there myself and have had no problems with them. But when it comes to something like this I have a whole lot more trust in the vendors on this forum than I do for the people working at Costco.