Went this past Feb and didn't do this tour due to the time on the bus. We did do Sting Ray City which I highly recommend but we booked it through this company:
http://www.sotoscruises.com/
They were about half the price of everyone else. It was intimate, professional and over all a great experience. High ratings on Trip Advisor is what made me book through them. I'd go w/ them again in a heart beat.