Thats a cool video but if it really works it would be great lot of four valve heads have hard to reach spark plug threads.
For regular wedge heads i think a regular tap is a better option. But i think pulling the head is best you can never know if you got all good threads or just a few left. Once the heads off you can put in a timesert. If the threads are really bad.
What kind of head is it. Or engine type.