[shamanNS]

@JWolf: Hint: Kindle for Android. I'm using that built-in function from the day one , so you don't need to teach me how it works.
Calibre's built-in apnx creation is part of the "Send to Device" process when sending books only to Kindle devices. It is not available for when I want to copy the same book to my Android phone , for which I would use "Save to disk" and choose "kindle" folder on my phone. So if I want to have page numbers when reading on my phone/Kindle for Android app (and I most definitely want that) I need to generate apnx file via this APNX Generator plugin (or manually copy apnx file from my Kindle PW1, at which point I might as well copy both the azw3 and apnx files form Kindle to my Nexus 4, and not use Calibre at all for sending books to my Nexus 4), which does not offer the ability to use page count from custom column. Because of that you get two different page counts for the same book, built-in generator used custom column value and APNX Plugin uses "accurate" algorithm.