I would wait till you get to the parks to see if you need them before buying them.We love express pass, but we stay onsite for the unlimited perk.If we had to buy them, I only would if crazy busy.May 16 and 17th is not projected to be too busy.Express pass is PARK specific, DATE specific and NON REFUNDABLE if your plans change.So wait till you get to the parks and decide if you need it.