I just acquired an Onyx M92 for PDF reading and so far, with my light usage, I am pretty happy with the reading experience. It is pretty speedy for page turns/seeking, in large, complex PDFs, at least as far as I can tell so far. Those same PDFs would bring my PRS-950 to a crawl (really unusable), so I'm very, very happy with my M92.
The only part so far which does not seem up to par is the the dictionary, which somehow displays English and Chinese characters. Also, after bringing up the dictionary, the initial display of the main text after the dictionary overlay popped up is not that great until you refresh the screen (icon in bottom right hand corner). I didn't use the dictionary much so far, nor did I use annotation at all, so perhaps someone else could chime in.
Another minor gripe: I would like a two page view, for books with one language on one page, and a translation on the next, but so far I could not find that option.
Dictionaries can be added, but it's not perfect (case sensitive, other issues too):
https://www.mobileread.com/forums/sho...d.php?t=178853
Having to use the stylus to navigate is annoying, but nothing that I didn't know beforehand.
So far there does not seem to be any firmware updates available for the M92 (I'm on 1.6.x, sorry, don't remember the full version).
I also have an Android 10.1" tablet (middle of the road Lenovo Ideapad K1), but personally I wouldn't dream of reading books on it due to LCD eye strain over time, though others might get a completely different experience using a tablet for lengthy reading.