Mizzanet,
We've only done a Progreso cruise excursion once, and we took the ship-coordinated bus tour to the Mayan ruins at Chichen Itza. Don't have any inside info about the Reef Club. But to be honest, on our stop, the water on the beach at Progreso wasn't very pretty, looked brownish like something you'd see in Galveston or off the coast of Louisiana. So to me, this would probably not be your best stop for a beach excursion anyway.
If you're *at all* interested in Mayan ruins, I'd strongly suggest a visit to Chichen Itza while here. You'll find an Excursion Review, with pictures, of Chichen Itza here on our site. The El Castillo Pyramid is awe-inspiring. And there are several other amazing structures to view. Truly a world-clspam place to visit.
At any rate, enjoy your cruise!

Smooth Sailing,
--Johnnie & Kim