We did a couple days diving there a few years ago, after our trip on the Caribbean Explorer 2. We unexpectedly had better diving on St Martin, due to great conditions at St Martin that allowed diving sites they couldn't usually go to (nice reefs, interesting stuff, pretty sharky), and assorted issues at Saba which was supposed to have been the best place on the trip. If everything were normal, I don't know what the diving would be like. Interesting island with lots of good food in any event, I'm glad we visited. Parts very built up and congested, but still interesting. (If you're into spa stuff, Ti Spa near Grand Case was an awesome little place. And that area is restaurant heaven, or at least was before the hurricane.)
We dove with Octopus from the Dutch side, even though we were staying near Octopus on the French side, due to boat problems. (Was unhappy about that since they still had one boat running from there, but I think it had classes so they drove us across the island each morning to the Philipsburg shop, but it turned out it was probably just as well. (Plus boarding the boat at their French-side shop looked tricky - Grand Case Beach apparently comes and goes, and was essentially gone when we were there.) A lot may have changed there since our trip, but it was a perfectly fine op, helpful folks. Would be good for novice divers, but I suspect that's true of anyplace there. If we get back there I might try someplace else depending where we were staying, I think I had originally been interested in using Ocean Explorers but at the time they were closed Sundays and that was one of the few days we had to dive.