Cozumel is an island and we've never booked an excursion - just picked a beach club for the amenities/features and enjoyed the day. Paradise Beach, Money Bar, Chankanaab, Nachi Cocom and others are popular and enjoyable, but very different.
First time in GC you should look for excursions to Stingray City - usually combined with a snorkel stop.
Not sure about the company you mentioned, but there are lots of options for stingray City tours discussed on the GC page.