When the extension is installed and configured it will automatically open URLs matching its list of keywords in pinned or private tabs and optionally close the source tab.
The matching URL itself will still appear in history etc, however it provides a nice way to automatically use a specific jump page for private browsing.
i.e. if a user dislikes google's tracking policy and they save "google" as a keyword, every time they open a page containing *google* it will be opened in a private tab. This has the advantage that the cookies are trashed every time the browser is closed without having to configure it in site-properties.
At the moment, it appears impossible to intercept the request before the initial page is loaded, therefore unfortunately the page will be loaded twice :(!