Here are my problems with such devices. I own an Onyx Boox 3 for a year now, I guess I qualify.
1) these screens still have bad contrast compared to a printed page at the same DPI. They mostly compare to yellowed dog-eared 50-year-old books. The dots are also rather fuzzy, so not really comparable to what you get in a decent LCD at the same density.
2) if it comes to desktop use, no OS/environment except classic MacOS up to version 8 and maybe GEM gives a shit about monochrome displays, especially those where only 1-bit colors look decent (so Windows 3.11 would likely count too). On DEs which you can still theme, themes that look like printed pages (two colors for UI, no gradients, no exceptions to this rule) don't exist at all. There's GTK's "High Contrast" theme, but it renders everything also BIG and FAT, which is cumbersome to look at unless you need it because of eyesight problems.
Also, there should be a way to disable all UI animations and most hover effects, but it either doesn't exist or keeps getting reinvented in any new major version so you're chasing it every once in a while.
3) Have you ever seen how Android renders colors on displays with no colors? God damn it to hell. I tried a terminal emulator. Some text was black, some white, some nigh-invisible, and some was white with a black (fuzzy) outline. I thought a monochrome display couldn't be ever described as garish, but now I've learned the errors of my ways. The only way it can work is if you export TERM=vt100 so it doesn't try to draw you rainbows where there can be none.
4) While the refresh speed got better compared to most Kindles I owned, when you're typing, it's still more annoying than a CRT with big afterburn.
Maybe it's kind of acquired taste, I dunno, but not for me. Yet. I hope.
I wouldn't mind a strictly 2-colored theme on a regular laptop screen as well, mind you.