Depends on the book. For stock digital graphic novels, it’s much easier on the Fold. For webcomics they are usually optimized for a narrower vertical screen. Same applies to static PDFs.

Text really comes down to the viewer. Assuming it’s a book format that can be reflowed, reading can be just fine. I still prefer the wider format so I’m not constantly scrolling or tapping to turn pages, probably helps with eye fatigue too but not sure how long you plan to read on your phone anyway.