I can't comment on the Adam & Eve kiosk, hadn't paid attention to that. I spent a lot of time walking the Club O beach, though, and spent time in the water there. I didn't see an issue with rocks until you got down to the area by the ruins of the chalets/Papagayo's, there were a lot of rocks as well as some debris still there, so that's where I would be careful. If you explore the ruins you'd def want something on your feet. I spent a bunch of time on the small beach on the other side of Papagayo's, the closer to the ruins the more rocks in the water. I did walk through the water in front of Papagayo's w/o any water shoes and I did regret that a bit lol...had to move carefully!
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