If you haven't already paid for trip, I strongly recommend that you check out Scubapanama, as well. Their rates for both lodging and diving are much lower, you're much closer to the two best restaurants in Portobelo (La Torre and Los Cañones), the lodging is better and you'll be much closer to the dive sites.
Both operators dive the same sites, and if the seas are choppy, there are only two or three sites you can get to. On the weekends, Scubapanama is sending out two or three boats at a time ... all four if they have a class.
Actually, if you can take the time to go to Bocas del Toro, I think you'll find better diving with Bocas Water Sports. I was shocked when I last dove Portobelo in September. While we did get to go out to the wall (calm seas in September) and saw a few critters and fish that I hadn't seen before in Portobelo, it was like all the reef fish (except Lionfish) were on vacation. Where I used to see Parrotfish competing for tastier morsels and lots of Sargeant Majors, Damsels, Butterflys and Angelfish ... there were perhaps two here and swim a ways to find another one over there. I think I saw a total of five or six lobsters and not one crab. (18 months previously, there were many of both, especially at night.) Yet, we were running into as many as five large Lionfish on one rock at the same time.
Our most recent dive trip to Bocas was in January. Lots of fish and critters. In terms of species, there may be more to see in Bocas than Grand Cayman. Much greater variety of dive sites and more of them. And, you won't find a better dive operator in all of Panama than Cappyjon and Bocas Water Sports. His divemasters are the best. You will definitely get the best value with BWS.