For anyone interested in e-Ink writing devices, there's also this "smart" typewriter:
https://getfreewrite.com
It's sort of at the very opposite end of the spectrum in terms of portability compared to the one shown by Onyx. And the Freewrite costs about $500.
I have one, and it serves its one purpose, getting first drafts out without distractions, very well. I also like the comfortable keyboard. Maybe the Onyx device will similarly serve customers with very specialized needs well.