I used an Kobo Aura HD (~2013 E-ink tech), with linux and is was almost fast enough to keep up with aafire. Using vim on a arm mx507 wasn't that fast anyway, so that the screen wasn't really a problem. It would have been a useful system for when you only stay in the console, switching over to firefox was a full screen refresh that needed a sec, so I tended to avoid it. Sadly I didn't get the USB controller to accept my external keyboard in its OTG mode, which was a hack in of itself, so I dropped that project again, but I still look from some time to time for a way to do it again.
Greyscale works as syntax highlighting, you do can get used to it after time. But what greyscale does to you is that isn't that interesting to you anymore to look at the screen, so you do start get "bored" from it and the eye starts to wander around looking for something else perhaps pretty to look at. Nice if you want to look often enough out of the window, but annoying if you have work to do.
For at dark at night coding it isn't that bad. But having an AMOLED with the right colourscheme and low lightness setting is more pleasing I found.