From the technical side, they run two 3.x kernel systems on their readers and the sdk was not touched since 2018. Which is why i bought a Android eInk, despite being from the same country like PB.
But i think they are more UI-centric and that part seems to be great, together with long battery life, stability and openness.
Way worse. Long battery live wasn’t a requirement for my usecase. PocketBook apparently holds weeks there. I you only want a reader, PB is the better choice. I wanted nextcloud sync (although there’s a community app for PB) and general hackability of the software, which is why Android.