Any newer 10" eink reader should be good enough for displaying b/w technical documents and A4 pdfs, by using its landscape mode (two screens per pdf page, with or without cropped margins), because we can even get a certain text magnification in that case.
New Onyx Boox (Air or Note 3) would be my choice since its native pdf reader is good enough (no need for installation of KOReader app), it has got a good pen and frontlight, OTG support for an external storage etc.
Dasung has recently released a powerful 10.3" eink tablet claiming that their newest refresh technology allows for almost no latency, but it is almost twice as expensive as Boox Air and it lacks pen support.
https://dasung-tech.myshopify.com/pa...ot-ereader-103
https://www.youtube.com/watch?v=0gEb4wWKSfo