Anyone have experience with booking excursion at the dock in Belize?

I have seen the people out with posters and descriptions of the excursions. Are they OK? What's the difference on cost?

I have not had experience booking at the port but I did have experience with Exotic Eco Adventures that seems worth mentioning. I had booked with them for a flight to Ambergris Key to snorkel Shark Ray Alley. We didn't anchor until an hour late and by the time I got there the flight had left. They offered me my 50% deposit in cash. I asked what other snorkel trips they had and wound up going to Goffs Key. They refunded me the difference in cash. They were very fair and accommodating and I would go with them again.