I beg to differ, when looking at biomechanics, I do not think it will have any effect on wrist movement at all.
Put on a thick chunky ring on your forefinger if you like (for effect

) and grab a guardless sword off the wall. Grip your fist tight around the hilt and rotate your wrist at every possible extreme angle and you'll see your fingers do not move at all, I don't understand what it could catch on?
I do think it is an ingenious addition that offers a sort of a rest function.
As these pieces were not always a weapon but doubled as a weapon and a machete, I know if I was holding it and chopping for hours whilst beating down new path in the jungles, my hand, wrist and forearm would want a break now and then between stikes.
I feel the ring hook offers at any point in time, a relaxed grip with the natural position of the forefinger, thumb and gravity allowing it to be held loosely in your hand and not falling to the ground.
Certainly in combat too, like hollywood movies, persons have dropped blades due to hard and well placed stikes, having this catch point where it is offers some chance of instant recovery rather than dropping the piece.
""I might add too, that in relation to a sweating hand and having this hook in place, it always keeps the hand in the correct place on the hilt in relation to the cutting edge.""
My $1.95.
Gav