I would never convert a CBR or CBZ to any format... a dedicated software will give you better results and functionality when reading. Specially on mobile!
For desktop I use:
Code:
CDisplay Ex http://www.cdisplayex.com/
If I have a PDF file with a graphic novel I do make them into CBZ: batch export all pages into JPG and zip.
Note: I do prefer single page comics with no blank margin... so sometimes I have to cut trim/cut the images with
Code:
CBZ MAKER TOOL - https://falsinsoft-software.blogspot.com/