To start with a confession : this bit came as part of a collection and my first reaction was to dismiss it as some sort of gimmick.
But when I looked at it more closely it is rather well made, all those complicated joints are smoothly finished and turn well. It is helpfully stamped with its name “The Wellep Bit”. It was launched in 1985 and although I don’t think these bits are in production any more the company web page still gives a lot of information.
Elwyn Hartley Edwards was very enthusiastic about the Wellep bit in his 1990 book “Bitting in Theory and Practice” and writes about it under the chapter heading “The Thinking Bit”. He explains that the cable which runs through the mouthpiece should form a “continuous loop” whereby the rider can feel the action of one hand with the other. He also praises the shape of the cheeks, the fact that it is effectively a “hanging” snaffle, and that it avoids any “nutcracker” action.
It would also seem that the cable could change the character of the mouthpiece. When there is tension on it the mouthpiece is quite rigid, but as it eases the joints can move and the central part acts as a roller which would presumably encourage the horse to play with it and to salivate.
I have read some quite positive reviews of them online, particularly for horses who were sensitive about their mouths.
No idea why they stopped making them – maybe they just looked too strange for most of us and I presume they were never legal in the dressage arena.