Trust the reviews, don't do this unless you have extremely flexible times.
I 'booked' for 9am on Wed.. they sent me an email confirming me for 3pm that day. That was not an option for me, no refund, they could book me the next afternoon when 4 of the 5 of us could go. We did that.
Guide was knowledgeable and helped us spot Bald Eagles, Manatee, Lots of Osprey including chicks and Adults carrying fish. He also explained the different mangroves etc. Was nice and good with kids.
We did the 6 person Mangrove Boat (not the bigger 10,000 islands boat)
He didn't know quite as much as he thought though... (You can't see manatees on the airboat tour.. we did)
We did do an airboat tour in the same day.. they had a lot of overlap, but were both enjoyable... you can't get much info from the guide on the airboat tour.. but it is more fun...would have been better to do the National Park tour first... so we would have known more on the Airboat Ride.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC