Just came across this old question and thought I would add my recent experience. After my iRex iLiad gave up the ghost, I got an Onyx Boox M92 (U.S. distributor here) and I am very happy with it. The screen is large enough, and the "hide margin" zoom setting works well enough, that I have never encountered a math PDF that I have been unable to read in that way.

(Those dratted computer science papers that are written in two columns with tiny font, on the other hand, are a little trickier. For that you can flip the whole thing into landscape mode.)

It is not finger-touch sensitive, but has a stylus that lets you make handwritten annotations on PDFs, then save a new PDF including the annotations. I use this a lot for editing my own work: I read it and make notes on the Boox, then export the PDF back to my computer where it is easier to flip through as I am making the changes. (One of the main downsides of an e-ink reader is the relative slowness of page turns.)

I don't end up reading DjVu files very often for whatever reason, but it does seem to read them fine. It is sometimes a little slow in loading a large file; I haven't tried any extremely large ones.

I do find that reading in e-ink with reflected light is noticeably more comfortable, and perhaps faster, than reading on a computer or tablet screen with radiant light.