Modern e-ink displays can update at about 2 Hz at highest quality and at up to ~8--10 Hz, possibly better, with reduced quality (more ghosting / lower resolution).

If usage is for reasonably static material and navigation tends to be via pagination rather than scroll, it works quite well.

Full video is possible, if of lower quality than on an emissive display.

I've written a set of my own recommendations for e-ink Web and App design here:

https://diaspora.glasswings.com/posts/638a8d10e041013afba844...

Mostly because it seems no one else had.