Unfortunately, this device doesn't solve a thing, and it's good that they're at least honest and didn't edit it out of the video. The deal-breaker here? Lag.

There's a reason people don't use tablets as paper even though they're almost ubiquitous, and perfectly able to act like it. It's because the few hundreds milliseconds it takes to react to user input is enough to make handwriting insanely irritating.

Interestingly, one of the recent Windows tablets (I don't remember the model; I had the opportunity to play with it few months ago) seem to have input lag so low, that you can actually write comfortably on it. So it's most definitely possible.