This Joomla - System Plugin, aims to minify the amount of duplicate URLs , solving the problem from its origin.
Kill Duplicate will assume that it is the only-one authorized to control canonical URLs from the Joomla internal variables. So, any other URL not matching the obtained by this plugin will be redirected to the canonical URL, using 301 redirect.
The plugin DOES NOT generate any URL by itself, but it manages an apropriate order to obtain them from Joomla router, that minifies the URLs variations and thus, the duplicated content.
The plugin DOES NOT replace the URLs in the Joomla pages, but it redirects duplicated ones to the right one.
The best option to get support for free extensions is the Joomla official forum, so eventually I may be monitoring the forum posts which include Kill Duplicate in the title to answer your questions.