[mcobrien]

Watching the video, I was struck by how slowly and carefully everyone was writing. I guess I might do that if I someone was filming my handwriting, but if it's to compensate for the speed of the sensor it's a problem.

Competing with paper and a pen is hard enough, but if you can't scribble fast it might be a dealbreaker.

[hastur]

It might have more to do with the lack of friction from the medium.

We're all trained to write by putting some minimal, but constant effort to move the stylus (pencil, ballpen) against the paper surface. Here, it's just a piece plastic sliding on a glass surface. You have to make a different kind of effort in controlling the stylus, when it moves too easily and has to be stopped or redirected at the right moment. (Learning to ice skate might be a good analogue.)