Many years ago I was friends with a member of the local dart association. He would do trick shots where he would throw the dart fins first and flip it in mid flight...while hitting exactly where he called it would hit. I understand how useful they would be as a distraction, much like pepper spray or a bright flashlight in the dark. I would never trust them as my primary self defense tool as that was not their role.
Looks like a fun way to pass the time though, especially if you and your buddies are slightly competitive.