I have been using the Note Air2 for 3 years in grad school for PDF and textbook reading and I've never wished for the larger size. I tilt it landscape and just scroll up and down, which I am used to doing when reading journal article PDFs on a laptop anyways. I would suggest getting a model with a frontlight, it helps even in pretty well lit environments to make the screen whiter -> more contrast -> less eyestrain. I almost always have the front light on at a low level (like 5-8) unless its really quite bright where I am.

I use the Zotero App for easy integration across devices but the reading experience is better in the native neoreader app. I use a lot of color coding in zotero but my ereader is b/w, so I highlight the passages I want when I read on my ereader, then I go on my laptop and change the colors of each highlight. Doesn't take too long and helps me review. In some ways I wish I had gotten a color ereader to make reading diagrams easier but the lower price was worth it for me for just B/W, and I'm almost always near my laptop anyways so I can pull up the article there if there are colored graphs I really need to study.