That's fascinating, I've often thought about how more films should experiment with non-rectangular framing but I'd never actually heard of this movie. It seems there was a lot of experimentation in the silent film era, as the rules of cinema had not yet been written.

Another example I can think of is the animated films of Don Hertzfeldt. He also uses masking a lot to frame his subjects, and often the frame itself will move or change shape within the same shot, or there will be multiple frames at the same time, like split-screen but with fuzzy blobs instead of rectangles.