Grand Turk doesn't have a lot available booked on your own - not that I can find, anyway.
We did this same tour last December. For some reason, the tour operator didn't seem to be able to stop where he wanted to, so we went over to the island to see the stingrays, first. That was my 4th stingray excursion and I'd probably rank it in 3rd place.
We got back onboard, and went back to being just offshore from Grand Turk itself, just around the point from the dock. I'm not a swimmer, and hadn't tried to snorkel before, so I was proud that I was going to finally get in there and give it a try.
Unfortunately, I couldn't keep my fins on.
By the time they got a pair that semi-fit, they were herding everyone back to the boat. I was pretty disappointed.
At this point, they haven't added the excursion that I want to do in GT (the horseback ride & swim - done it twice and love it), so if that isn't an option, I may try this excursion one more time. Or I may just lay on the beach!