We’ve been to Club O a couple of times, and just got back from Mak Nuk. There is really no comparison. Club O is on the beach, rustic, and on the French side of St. Martin, while Mak Nuk is about a mile from the beach, is a luxury condo hotel with an incredible pool, and in the laid back town of Tulum, Mexico. Here is a link to the trip report that I wrote on a Tulum forum. Hopefully it will answer some of your questions about Mak Nuk.

http://tulum.info/forum/topic/it-was-a-warm-rain.9025/