That’s a clever way to do it because it cuts the load on the shackle 50%. I don’t like how it’s tied to the crossbar cleat. Putting it through the middle and around both horns would distribute the load better. Personally I go from the bow cleat down to the ball and back to the crossbar cleat as that cuts the load in half on each cleat and gives you a 4 point attachment to the boat.
G