Here is a tip...FWIW. Call the night before and confirm. (I do that wherever we go, cause I want to sleep till the last minute and I am usually bugging them to be picked up last, he he) On a Waikiki rush-hour am route, you could be gaining almost an hour of sleep, plus you are "confirming". I never go to an appointment without calling because usually I am the one that messed up the dates or the time.
I would ask about the boats, if you care. If you are being farmed out on another operator's boat, that is useful information. It is not always bad, but for me it tells a lot about how much control they have over where that charter will go. You are in a group of two and get booked on a boat where another operator has ten? Guess what? The boat is going where they want to go. (if you care)
On the other hand, lets say you have booked with a boat owner...take Diamond Head Divers, for example. If you are diving with him for the week and have requested a site, he most likely made a note of it and feels more responsibility to your dive agenda than for the guy another operator has booked where he is only getting about 30 dollars for the the boat seat.
Another important question to ask: Is the boat on a timeline? Is the boat hustling back for the second charter? at what time? Some charters are rushed, others are not.
I prefer different operators for different reasons.