Have you used before an e-ink keyboard?
I found an ultrabook or 2-on-1 tablet (I don’t know exactly what it was) with e-ink keyboard and I was expecting the best. But after just use for 2 minutes, I found this is not for me. You see, I use the 10 fingers from both hands to type, and do that on e-ink keyboard is a nightmare, because :
Normally to type you rest your fingers on asdf jkl; keys on a physical keyboard and then press on the sequence of letters you want to type. But you can’t rest your fingers on e-ink because it will type . Second, the e-ink refresh rate is slow, so you will never type 80 words per minute with that kind of keyboard.
Ok, I know, it is not a typewriter, but the point is the simple keyboard shortcuts like Ctrl-A (to select all) + Ctrl-C (to copy) is slow on e-ink keyboard. At least on that e-ink keyboard I used.
E-ink keyboard is fragil, not as a physical keyboard.
But a secondary e-ink Display it’s another thing, especially on a phone, will save battery and your eyes.