We didn't do the Caverns & Caves, but did do the Secret River (somewhat similar I believe). It was one of the best excursions we ever did to date, but we love doing the more of the unique things. It was a great, and yes I would go back.
With that said, don't let what I am about to tell you influence you from going, because for us it was well worth it...BUT I would be remiss if I didnt mention one big not so great thing.
Please keep in mind, that ferry ride over to Playa de Carmen is not for the weak of stomach. Seriously had roller coaster ups and downs with back and forth rocking. We all started taking Bonine 2 days before the excursion, we didn't need it for the cruise itself, but did our research. We researched the excursion on TA and other Trip report sites.
All the reviews said the same thing "ferry is a roller coaster". The operators even hand out airplane sick bags to everyone if you think you need them or not (take it just in case). They have large garbage cans that are easily accessible. They did the same for our trip. Again this is not to say some have better experiences with those waters, but we were in the majority of rough water in the morning at least. It has something to do with that stretch of water. The Ferry is nice enough, at least the ones we had. They were larger ferries which had AC, cushioned seating, and bathrooms. Many people did get sick, but they admitted to not knowing or just dismissing the reports, thinking it wouldn't be so bad. It can be bad, and IMHO better safe than sorry.
My DH gets very seasick on smaller vessels and has even skipped a Palo Dinner on
DCL once. That said with the Bonine he was OK. I don't usually get sick on cruises and neither does DS, even rougher seas, but to be safe we all took it. We all did fine. However, we were glad the ferry ride was over though, most likely a mental thing and DS was just spooked a little bit (he was 7 at the time). By the time we got to the excursion we were totally fine. We hated getting back on the thing to the Cruise (again mental thing), but it was a little better in the afternoon.
Everyone has different experience, so might not be the case for your trip, but overwhelmingly we found above to be true, from reviews, friends that ventured on similar crossings in this area, and our experience.
I would definitely do it again as they have 2 other rivers to explore, but I would take sick meds as noted.