I've never seen anything like this, but it definitely has leverage to it and looks like it applies quite a bit of pressure to the nose and the mouth simultaneously. It also would not slide to either side I guess because of being boxed in. I wonder if this was somebody's training solution??
It looks like some really old fashioned home made hackamore/bit combination. Applying pressure to the nose as well as the mouth. The big metal pieces would help with turning, instead of just the cheek piece on the bit - it has the whole plate to help push the horses head around.
I can't imagine it sitting to well in the horses mouth, and I'm guessing that chain in the bottom photo goes around the chin and hooks up to the other side.
If it was a little better made (different angles etc.) and softer padding, it wouldn't be that harsh of a bit (of course depending on the riders hands)
But yeah - wouldn't put it near any of my horses that's for sure!
Definitely looks homemade, and poorly planned out- either the mullen mouth part sits in the mouth backwards (curving inward) or the hackamore portion sits over the delicate part of the nose... Either way, I feel bad for any horse(s) this was used on!