I read that they were used frequently in Indonesia and Maldives. Is that not true? Even on Scuba Board people talk about using them in Indonesia. See
this thread.
I did use a hook when working as DM/Instructor at Maldives in the eighties.
It was a tool to be used when doing a specific type of dive, which I did not see anywhere else.
That was Kandu Diving. Kandu in Maldivian (Divehi) means a deep channel in the outer reef of an atoll.
We did usually dive in channels where the current was flowing inside the atoll.
You splash a few hundredth meters outside the atoll, where the depth is some hundredths meters, and swim down to the same depth as the edge of the channel (which was usually between 30 and 50 meters).
The current brings you quickly towards the channel, with speed increasingly due to the Venturi effect.
As you see the edge of the channel, you try hooking the edge and to get a stable position on it, looking towards the external side, where big pelagic fish swims around.
On the edge the current is incredibly strong: without the hook it is almost impossible to keep a stable position.
There is no live coral on the edge, so no risk of damaging it with the hook.
However, when doing other types of diving, such as following a reef being transported by the current, no reef hook was used.
And when at the end of the drift dive you launch the buoy, so that the Dhoni comes and launches the deco bar with additional deco tanks, of course you are not hooked.
It would be impossible to launch a buoy while hooked.
Instead launching the buoy is easy if you are drifting together with the current, as in practice, doing so, it is as if there is no current, as you are not moving relatively to the surrounding water.