Just a warning and from experience don't try and look through the glass bottom when boat is moving, it makes you very queesy. The trip is excellent, especially if they moor up for swimming, lovely to swim in the deep clear water, go prepared, take your cozzy.
We tried this trip years ago, unfortunately it wasn't very good weather very windy so spent 2 rather boring hours being tossed about watching people throwing up off the back of the boat with no glass bottom viewing, only good thing was it didnt rain.