"You will hit your hand" is one of the most common statements I get as comments on my videos. It actually happened a few times. A band snapped at the wrong moment, at release, and the ball went slightly off, for example.
Just for fun, I designed a cuff that protects your hand. This model is for hammer grip style shooting, but of course it can be adapted for the finger support style as well.
The leather is 6mm cowhide, bought a ton of it on ebay. It is very tough, no slingshot ball can penetrate it. Can't make a full glove from it, it is not flexible enough.
I can and will optimze this further. Velcro comes to mind, or rubber.