I did the submarine safari a couple of years ago. It was an experience but unfortunately not a lot to see once down there. They feed fish so they come close to the sub and there were also a couple of divers that went out to entertain you.
Saying that it is something you will probably only do once. We got certificates for going too as well as the obligatory photo as you board.
Hope you enjoy it.

Have done this submarine trip before they restarted the new one , good expeicance and well woth the money