Correct me if I'm wrong, but I examined the code (after it failed to retrieve the *exactly duplicated* posts) and found out what the plugin does is basically get ALL of your posts in the database, and run through ALL of them in a loop, breaking the words and compare them one by one with each run. Being a WP plugin author myself, this isn't exactly something I would do.
My site has ~6000 of posts right now, and this causes a really memory issue. If you have a relative big site, you may want to reconsider about using it. Otherwise, it still works great.