I got these cool little gems from Ken's Bolt on Grab Hooks. These hooks are like no other I've ever seen or used. They have an ingeniously simple latch that's way stronger than the typical stamped tin latch you see on most hooks, to include cranes. These have a robust locking mechanism that's spring loaded. No matter the situation or amount of twist, these will not let go of the locked-in chain in the hook. Very cool.
I bought a 20' 5/16" towing chain with a 4700lb working load limit from Lowes ($37). I had them cut in in half at the store for free and proceeded to install these new hooks. So now I have 2 10' chains with a grab hook on one end, and a twist lock grab hook on the other. All you need is an 11/16" wrench/socket to assemble the hook.
Here's a couple of shots of how the twist-lock works.
These won't let go, no matter what.
I'll tell you something else too. Ken has a bunch of other goodies on his site that I didn't know was there. He's been adding all kinds of cool stuff like the Ball Dog.