I think it's very smart to go in a small group with a local guide, that way he has no trouble keeping track of everyone. The problem with the cruise ship tours is that they come with boats that probably hold fifty people and there will be several of them at one spot at the same time. You can imagine that it would be easy to lose track of someone.
Tulu has a small boat and watches out for his clients. I'm sure most guides will do the same. They also know when areas like Hol Chan or Shark Ray Alley will not be having cruise ship crowds. We have seen times when you would swear that there are more people than fish at those two stops. Go and enjoy, just be smart.