So a very late update to this. We got on the second tender but the process was maddeningly slow.
Regardless, the tour guide was patiently waiting for us at the terminal and the tour was very good. Our guide (I believe his name was Vel) was excellent and got us to parts of the ruins that the bigger tours were skipping. Lunch was included for us, at a local place that seemed to just have "Diner" on the sign. Very simple food (stewed chicken, rice and beans, coleslaw) but very flavourful. Probably not something you'd normally get, but it really hit the spot for us.
At the end of the day, big thumbs up for King David tours. Might try them for a Xunantunich tour next time we're in Belize.