I was originally thinking of getting a BOOX or so after my old tablet died. In the end I went with a Lenovo that was on sale instead, and that was a good choice.

I just don't have the use case for them, much as I love their screens. I already own a Kindle, so maybe I'll look into the BOOX again if my Kindle ever dies and I need a new reading device. I will say that I cannot imagine reading on an normal screen after reading on a Kindle for a while. There's so much eyestrain from looking at a lit screen compared to the more paper-like e-ink display. An important thing to note is that my current Kindle came with the back-lighting set up all wrong:
It was set to behave like a mobile screen, getting brighter the lighter the room was. But that's not how you'd use it IMO. I now set it up so it's off when it is bright, and dimly lit in the pitch dark, so that when there is external light it behaves exactly like an actual paper page, and only when reading at night in bed is there any backlighting so I don't have to keep the lights on.