In the commonly used type of safety razor, the axis of the handle extends at right angle to the longitudinal direction of extension of the blade. The natural and most convenient mode of operating such a razor is to pull it across the surface of the face in a user experiences more or less discomfort.

Otto Spahr in US patent 1,639,441

Reading the introductory paragraph of Otto Spahr’s patent, I get the feeling he could be a bit snarky at times. But he has a point – the common safety razor isn’t the most ergonomic design. And if you’re using the “Gillette Slide” – which some sources indicate was a common technique – it was even less good. Possible solutions includes the slant, an offset handle, or having the head at an angle to the handle.

Mr Spahr picked the later approach, and seems to have gotten the idea that no set angle suits everyone. So he came up with a design that allowed for near infinite adjustment of the handle. In the words of the inventor:

Another object of the invention is to so hinge the razor-carrying frame to the handle that the handle may be adjusted to any desired angle to the blade, so that the axis of the handle will not only extend at an oblique angle to the longitudinal direction of extension of the bla e, but maybe within the plane of the longitudinal centerline .of the blade or at an angle to such plane, as the user may prefer.

Otto Spahr in US patent 1,639,441

A spring loaded ball joint meant that there were no screw threads that can seize up. The spring pressure must be calibrated, to stop the handle from either being beeing too stiff or too loose.

While not an adjustable razor per see, Spahr’s razor offers opportunity for a lot of adjustment. I can certainly see it being of interest for people with less than full use of their hands, for one reason or other.