I'm sure it works, Andrew, but that chain restraint seems mickey-mouse to me, and puts shock point stress on the cast pump aluminum gear housing and bending stress on the PTO shaft, since the pump is so far out with no support.
On the backhoe, which also has a PTO driven pump, it's bolted securely to the tractor frame. Now I realize the point was to make the pump more easily removable in this case, but a chain? There are plenty of ways to make solid, but removable attachments -- hitch pins for instance, seen on, well, practically all tractor implements. Or they could have mounted the pump solidly on the flail frame and used a universal PTO shaft.
Failing that, if they insisted on a chain, gosh why not two? One on each side. That would have prevented the damage from a mistake and restrained the pump in case one or the other chain had failed.
Apparently saving the cost of another foot of chain was worth more then the damage of connecting it to the "wrong" side". Or in the case of a broken chain or casting (a distinct possibility) the effect of a flailing hose and chain on a farm worker.