We also have a card that has access to lounges all over the world at various airports. It does include SXM. Have used it a few times, not sure I would pay for a membership unless you travel enough to make it worthwhile.

The ones generally with the card are for the cardholder only and a set fee for the second person. Depending on the lounge it can be a good discount, but not for SXM as it is actually more than if you pay directly for the second person.