Very nice homemade grapnel. I made one with some 1/4" j bolts and an eye bolt from the hardware store using 2 part epoxy as the bonding agent. Sometimes I'll stick a large rare earth magnet (1"x1") on the bottom to add weight and increase the chances of grabbing the bag. Just be careful using the magnet around camera equipment...
My version can be seen briefly and in action at 5:11 in the attached video link.