It's kind of like taking
but then filing a notch on the center, but... I dunno. This is the description:
The Victory also has a pinch-free, two-pronged guard, which gives your thumb joint more room to bend and provides a more stable hold on the string (the string rests across the dimple, which mitigates unintentional up/down rolling).
Another grooved ring
The description:
Our string groove is a subtle aid in string positioning, and does not allow crimping of the string nor is disruptive of the release. This strikes a good balance, allowing those who prefer the help to have it, while reinforcing good form.
Their description of the tongued ring:
The tongue ring is another historical oddity out of China which, up until now, wasn't really accessible to most archers. The string actually rests on top of, as opposed to in front of, the protruding tongue. In use this presents as being somewhat like a lipped[guarded] ring, in that rearward string travel is limited so the string does not dig into the soft part of the thumb, however upon release the string abruptly drops like a hammer off the end of the shelf resulting in a distinct and snappy release. Until partial draw is achieved, the archer must either slightly angle their wrist or have the skill to balance the string on the tongue, before the natural step of the ring kicks in keeping the string off the thumb.
If the string is balanced on the ring as such, I suppose more of the force would go into the ring, and the joint of the thumb. Then the string wouldn't dig into the thumb because the force's against the edge of the ring. or 'tongue', in the case of the tongued ring.
So it's kind of like in pic 1, but the thumb is more bent, but angled such that the force goes into the ring and not pinching the skin.