Interesting videos, could soon be some competition to the Harmonic drives.
https://www.youtube.com/watch?v=IXmCze1GsGU
In the second video showing and testing 3D printed vs CNC machined alloy there is a mention of the producer accidentally ordering the discs powder coated and having to sand it by hand to remove the coating from the contact surface of the discs. That is the most likely cause of the differing backlash in differing positions.
Still, interesting videos and very smart gentleman making the stuff.
https://www.youtube.com/watch?v=mPwbDrXq50Q
Caveat: the subtitles do not have a high level of accuracy but most will understand the gentlemans English.