Maestro cards do not work at most point-of-sale terminals in the United States. You're going to be limited to ATM access.
Maestro is simply the debit version of MasterCard. He's claiming they are MasterCard, although he could just be dancing around it since Maestro is in fact Mastercard's. What would be nice to clarify would be if OP could
take a picture of one of the cards and post it here. As a point of sale developer with some experience in retail management and having lived in Korea using American cards of all types, I think I'll be able to tell if these cards are worth anything just by just seeing them.
I don't want to expose the bank in public view. I will do this on a case-by-case basis. They are Maestro cards. I emphasize MasterCard because most of the Americans may not know what a Maestro card is. If someone wants to see it, PM me and I'll take a photo, blank out the account number (I'll be taking a picture of my card).