The latch with no hook is for all sandcasts.
This hook-less latch afforded single action, i.e., the cap did not need to be held down prior to depressing the thumb latch in order to release the cap.
The problem with these single action latches, the pressure exerted on the latch to release the cap could break the latch, it's still a good idea to press down on the cap to relieve the tension on the latch to avoid latch breakage.