Thanks for the replies.
We ended up diving with Seasports Belize. Unfortunately, we had a very disappointing and unsatisfactory experience.
The equipment was low quality and in poor condition.
The tanks were not completely filled. Some were 2600 psi.
The boat was quite small, which isn't necessarily a problem, but the captain beat the crap out of us going over swells. Over a month later, I'm still undergoing physiotherapy for injuries to my lower back.
The first dive was okay, but on the second dive, due to the large swells and current, the DM instructed everyone to go down the anchor line, then submerged from beside the boat, away from the anchor, resulting in the group getting separated. (The two divers who decended the anchor line ended up surfacing alone when no one else showed up at the anchor.) Once he finally collected everyone who stayed on the bottom, we followed him around in the sandstorm, until he gave up trying to find the reef wall. 30 minutes after we submerged, we surfaced a long way from the boat and had to do a tiring surface swim against the swells.
I complained about these issues and the shop compensated us and promised to take serious measures to address the issues. They also offered a discount in case we return to Belize. They also promptly mailed my fins to my home after I left them in the boat. I give them credit for their response, but the experience was overall very disappointing.