We did this excursion last month and it was perfect for us. We had our 2 adult children (20yo & 24yo) with us and they loved it as well. You walk about a mile or so with a tour guide who stops and shows you different things native to the island such as plants, trees and such. You end up at a private beach and you kayak into the native mangroves and thru a waterway and back. My DD and I had never kayaked before and we got the hang of it quickly, even tho it was extremely windy. Would totally do it again!
It does take up several hrs out of your day. Ours started at about 1pm and ended at 4:30ish. So by the time my family did the 5k in the morning. Then snorkeled for awhile it was time for lunch, excursion and back to the boat. If you want some quality time on the island to swim and lounge then this will take up a lot of that time.
But now that we have done it, our next trip we will spend just enjoying the island and all that it has to offer.