We booked the 4 hour tour that we really enjoyed with less than 20 people on the boat. The driver was very knowledgeable and entertaining.
During the whole trip there was enough Pizza, cool water and also alcoholic beverages like prosecco and beer for everyone on board.
We also made a stop in the middle of the lake and everyone who liked could go for a short swim. You won't be able to change your clothes on the boat, so be prepared for that.