This hydraulic brake was produced by Mairag, a Swiss cycle company. I found this on Classic Rendezvous, a website focused on lightweight vintage bicycles from 1900 through 1983. The site is broken into countries of manufacture, which makes it fun to browse. Mairag came to be in the 60’s, was owned by the Maier brothers, and was based in Ebnat-Kappel, Switzerland. It’s hard to tell from their website, but they still seem to be in existence. Interesting designs indeed.