[Ansileran]

Ok, so the list I gave is pretty much what I think is missing from all / some of my devices.

The PRS505 (Sony) does a very good job with text pdfs. It's slow but I don't mind. Of course, it doesn't have a good screen quality (compared to the Aura HD), no front light, no dictionary... My mom's using it so I don't want to take it back from her.

I don't really use the Odyssey (Cybook) due to the poor screen quality. I don't think it does any better than the Kobo with pdf anyway. The different options for browsing books are nice though.

I could give up on reading pdfs, or decide to buy the M96C, but that would be for a different reason entirely. If it were a color e-ink screen, I wouldn't hesitate, even with washed out colors...

Kobo doesn't do that well with dictionary.
First of all, the list of languages is very limited, unless you want to do some annoying tweeking: passing off your dictionary as a different language, then changing the language of your ebooks to match that language...
The French dictionary is pretty good, so is the English one, however I cannot search the English to French dictionary (or the French dictionary) outside of a book (or to search for the meaning of a word in a pop-up definition).
The German-English dictionary doesn't recognize "declination". If the word in the text is "Menschen", a good electronic dictionary should recognize that this is the word "Mensch" (a man). The monolingual dictionary did find that one, but didn't pick up on some irregular verb forms. The German to English dictionary is not that good, and of course no German to French dictionary (but that's mostly ok)
I do need rather big dictionaries, at least for the monolingual dictionaries, as I've started reading historical fiction and old books where I'm not familiar with some of the words (French dictionary is good for that)

The text notes (those ref links you can click on) don't show in a pop-up but take you to the linked page. Most of the time, if you use the button to go back (don't know what it's called in the English firmware) it either doesn't work or closes the book. I've had only one book (in a hundred or so) that worked properly (no kepub, epub only).

My Kobo is a French one, Kobo by Fnac, so the firmware might be different from the actual Kobo one. It's linked to my Fnac account which pushes previews of the recommended books to the device and have them show in my book list. Maybe something is wrong with my account set-up there. I sync to get firmware updates, not books...

Pocketbook looks like an interesting option, with the ABBYY dictionaries. What about front light quality? Looks like the Ultra is available here for around 150€...