Detailed Documentation is coming.
But in the meantime, the pro version basically adds some new features such as:

  • the ability to have content that is displayed only on the print page using a print_only attribute
  • a custom printer icon can be used by uploading it to the media library direct from the options page
  • url attribute to print an external page
    • example: [print-me url=""]
  • css_url attribute to load an external style sheet into the print page
    • example: [print-me css_url=""]