You should be fine. Cozumel is completely different from Bonaire in many ways and with those two locations under your belt you should be fine. And, if for any reason, you don't feel comfortable on a dive, just call it and get back to the boat. It's no big deal.
We did drift dives off the Nekton Pilot at Cay Sal and Nekton Rorqual at Medio and they were fun. The group goes in together with the a DM with a marker bouy in front, and another DM following the group. Everyone stays together and then does safety stop together. Once everyone is up, they signal the boat and it backs up close to the group. In pairs of two, the divers swim to the dive platform and the crew helps them get back on. It is really easy and well organized. The Cay Sal drifts were true drifts where the current was strong like some dives in Cozumel. The Medio drifts had no current at all but we did them as drifts because there was no mooring pin there yet.
We are booked for Cocoview for Nov, otherwise we might consider this trip ourselves. We have been thinking about doing the St Croix trip, too. Both our Nekton trips were fantastic and we will do more trips with them in the future!
In fact, this past weekend my hubby was teaching OW class here and a student and a DM wanted to discuss the Nekton with us (they all read our website, trip reports, etc.) and think those are perfect trips for their families (both have Jr diver kids as buddies). I told them I think the Bahamas trips (NW and Medio) are perfect for them and their young diver buddies to get more experience as well as perfect for the Dad's as if the young buddy is too tired to dive, they will be able to buddy up with another diver on the boat and go!
To me, the Nekton trips are incredible for new divers and experienced divers, especially in cases where they are traveling together. On our Medio trip in April, we took one of my hubby's DMs (who had been diving 20 yrs) and his new wife (who has less than 50 dives). Both had a fabulous time and both went on almost every dive. It was a great experience for both of them and they are both hooked on the Nekton!
I know there are other liveaboards out there that are prettier, or more fancy, but as far as I am concerned there is none better at what they do. The Nekton always delivers fun, great diving, lots of diving, lots of fun, roomy boat, crew that is second to none, and ......
robin