No you can read them fine using comix if your eyesight is okay, If not you can customize comix so it fits the pages to the screen in a way that's best for you.

I've installed cbr pager which is stable and works well but it has fewer options than comix.
The default reading mode for cbrpager will be fine for everyone. The page zooms in to fill the screen horizontally and you scroll vertically to see the bottom of the page that you're reading.

Portrait mode is enabled on both comix and cbr but again, comix has more options for portrait mode viewing.