I believe these are only for utility poles. My friend, a former lineman, explained to me that they would climb the pole with pole spikes and their hands, when they got in place they would put their belt around the pole.
If they tried to climb a pole like a tree, with strap in place, hitchhiking with a scarestrap, as he put it, they would spur out and not be in a position to grab the pole. The pole is smooth and a strap doesn't grip it. They would just slide down it. He said he has known people the have gotten splinters under their ribs.
This seems to cinch around the pole, arresting the climbers' fall.