I vaguely remember my grandfather years ago using a similar implement to brace a mirror while he installed it. I don't remember much of it, but what I can recall is that it was old, and it still worked so I would imagine the discs on it were also old as well.
Yours is in remarkable condition, and those discs look almost like they've never been used. The patent describes the discs pretty well, and they seem to match the description. I understand there are a lot of variables that affect the fatigue of the rubber, but maybe they were preserved somehow?
Anyways, very cool tool that you have there. I also did quite a bit of searching to find out more information on it, and haven't found much other than it seems Henry G. Lange produced quite a bit of machinery, ranging from grinders to auto glass installation tools.