Hi, the manuals says both Pocketbook Inkpad 3 and 4 supports cbz:
https://www.manua.ls/pocketbook/inkpad-3/manual?p=13
https://www.manua.ls/pocketbook/inkpad-4/manual?p=13
I'd liked
this video review, what I'd liked from the 4 is the glass water and scretch resistant screen (don't know about the 3), has physical buttons (on the bottom, not on side), has a very nice integrated cover attachment, within magnets closure; doesn't has microSD but 32GB are quite some space (but imho); althought it seems a little more weighted than predecessors (262gr vs 210gr), darkmode on defaults' availability (white text on black backgound).
The review explains the Company did spend its effort to optimize user experience and firmware.