I don't ride horses or shoot bows but watched anyways. You never know when you're gonna need to string your first horse bow haha

The Ming Chinese thumb ring you showed is supposed to be used with a shallow hook with the string in that groove

My favourite is the Turkish thumb ring

Spur ring. I've heard said that the spur helps with modern Mongolian style shooting thumb from the inside of the bow. The spur keeps the arrow on the left. Not experienced this personally.