[j.p.s]

Originally Posted by Tarana

PW3 - glass substrate

PW4 - other substrate, light/dark modes, more storage space, link to bluetooth to play Audible audiobooks, waterproof.

PW3 is a pretty solid ereader. Unless you need these other additions, no real reason to upgrade. My sister's bf reports that manga shows clearer on PW3. This is but one person.

Both the PW3 and PW4 have a glass substrate.

The PW4 display is flush with the bezel and the PW3 display is recessed. Many that have used both say that text looks sharper on the PW3. Some of those say the PW4 is still good enough to read on.