The bar itself is rigid, but it can twist in ALL SENSES.
I finally find that the important thing is not so much the rigidity of the bar as the fact of attaching his line of line to the gallows of the bike (very important). The bar helps keep the line on top of your wheel before any conditions.
If the bar breaks for any reason, your dog will remain attached to the bike.
A flexible bar allows to have a radius of bending of 180 °, to accompany the movement of the dog and to give a margin of maneuver to the pilot of the scooter.
Questions ? Let me know.