This is a challenge for a German speaker. The Wayback Machine shows that Sasse series 25
(the one that contains Sasse 200MN) used to have a switch with a four-legged black thing:http://web.archive.org/web/200311020520...tur-e.html
Now, maybe half a dead spider fell into the photo when it was taken, but to me it appears to have the same style pre-Berlin Wall era Hall IC that RAFI use. (The HFO on RAFI Hall ICs denotes Halbleiterfabrik Frankfurt (Oder), I finally discovered!)
I never got anywhere with Sasse (or any of the distributors from that era), but maybe a German speaker can be more persuasive. Someone must know something about these switches. If it's not Hall effect (which is not mentioned on the website), then what on earth is that thing in the photo?