Hey, TechStuf!
I just built a sling using your wire release hook. I was cheap, I just used 12-gauge bailing wire. Here's my first impressions:
This is not a sling for general use, it takes too long to load it.
It is rather heavy. Noticeable pull on fingers after release, which is something to get used to.
I'm consistently releasing LATE! I think I need to work at the release gadget with some pliers. I believe the angle and curve of the wire is critical to a good release, and I've got them wrong. Then I need to polish the wire, I can feel the release ring catching on the wire.
FOLLOWUP: the shape of the hook is not as important as its smoothness. I finally gave up and made another hook, and I was careful not to mar the surface of the wire. Even though it is not as well shaped as this one in the picture, it releases much, much better.
If you want, I'll scan the sling and post the photo.