By the way, an alternative to reading cbr/cbz on the Pocketbook is to generate an epub with images optimized for the screen resolution and shades of gray.
I use KCC/KindleComicConverter https://github.com/ciromattia/kcc
which works great for the pocketbook 912 (pick the Kindle DXG profile in the popup).
The generated epubs work both with adobeviewer (which sometimes crashes) and CoolReader 3 (which doesn't crash on these, and seems a bit faster).
If you use CoolReader, make sure the page margins are set to 0 in the settings (they are 8 pixels by default).
KCC (which is based on mangle - mangle generates optimized cbz) automatically cuts margins and page numbers.
The only disadvantage is that you have to convert each cbr/cbz to epub before viewing.