We bought tickets online 9 April, departure South Beach 10.45 and return from Bayside Markedplace 13.00.
The 10.45 departure never showed up. When the next water taxi arrived at around 12, the captain couldn't accept our online order at first and had to call "the office" several times. I too called the office, and it was finally solved. Several other passengers had problems too, and it took like forever to leave the dock.
We had to reschedule our return to a later departure, as our time plan got messed up. As we had to get back on time, we decided not to rely on this amateur service provider and mailed our cancellation 1 hour and 22 minutes before departure, which would enable Miami Water Taxi to accept other passengers in the queue. I stated that we wanted a refund for the return trip, considering that the cancellation was due to their extremely poor service. I have heard nothing from them at all, despite following up with several mails.
To be fair, the trip itself was nice, and the captain really tried his best - he just had no authority to decide anything and seemed to be remote controlled from "the office".
If you don't mind wasting your time waiting and not being able to rely on the time schedule at all, go ahead and enjoy the ride. Elsewise, take an Uber.
I certainly don't recommend Miami Water Taxi.