I'm using this plugin on a site that lists both the numerical navigation (1, 2, 3... All Pages) and previous/next links. Since this plugin applies to all wp_link_pages(), the All Pages link showed up in both navigations.
With this small patch ( http://diffchecker.com/mvD7u0k7 ) I added a check to see if 'show_all_link' was set to false. If it was, don't include the All Pages link.
I can then build my navigation like this: https://gist.github.com/2718947