I took the water taxi from San Pedro to Caye Caulker and back one day, great trip.
The water taxi is not like a cruise, it is just the means to an end.
You are stacked in like sardines, traveling north sit to the left, traveling south sit right, less water being sprayed on you.
I find boarding tricky, stepping from the dock to the boat that is lower, and the boat bouncing, sure tricks the eyes, therefore I need someone's hand, and another passenger had to help me. Remember the Captain and crew of the water taxi is not as accommodating as your snorkling and diving guides. You are on your own. But HEY what a trip, it works and is cheap.