There are directly ekink monitors now.

Dasung 13k color is workable-ish even on MacOS with no tweaks.

Well this is no replacement for them! The monitors you mention are from 700$ (Dasung 13k is 750USD currently) up to 2000USD. This is an old tablet you maybe have lying around or can get for 200USD maybe?

And this is more than a monitor. the VNC provides you with an interface. you can use your tablet as the input device. and it's also portable.