Here is why I MUCH prefer the One:
https://www.mobileread.com/forums/sh...&postcount=181
The One does allow me to read PDFs I couldn't read otherwise, though it could do much better, but the main reason why I would find it difficult to go back to my Glo HD or even the H2O is that I find it much more pleasant to read a book with a decent "real estate".
It seems to me obviously better for poetry or any fiction or non-fiction with long sentences. Sure my preference might have something to do with my aging eyes - by the way pajamaman we retired old folks are not a "smallish" sector for the readers market: all the studies I've seen show that many young people read on phones or tablets or computers, and most don't read all that much, while retirees like me have time to read for hours and eyes that don't tolerate backlighting. And some of us love Kobos for the possibility to add our preferred fonts and play with their thickness.
For me love of litterature is also love of good typography, and you need space to make a good-looking book.
Before readers, I went from mass paperbacks to trade paperbacks for my favorite books, and even bound books for those special ones, just because they deserved good typography, and it made reading them again so much better. I belong to the re-readers. For those who read French, I recommend "Relire" by Laure Murat.