The pain kinda disappears if you have a physical Kindle. You enter the serial number once during setup of the plugin, then download the books from amazon.com/my

The pain kinda disappears if you have a physical Kindle. You enter the serial number once during setup of the plugin, then download the books from amazon.com/myk ("Download & transfer via USB" option), and just drag-and-drop downloaded files into Calibre's interface. Works on Ubuntu too, which is really a PITA otherwise.