You can easily load PDFs into kobo readers, at-least into mine. However, most PDFs will be unreadable. To reads PDFs properly on a e-reader you need a screen that is at-least as big as their render size. Meaning, that if the PDF was built for A4, your experience will be, in most cases, lacking on any screen smaller than A4.

I have no experience using such big eink and can’t comment on their quality.

Bought a math book from them, they refunded it with no questions, after I read a lot of it, because some of the equations were unreadable.