The faulty approach video was a typically crap American if-I-say-it-loud-enough-it must-be-true type video. I don't agree there are three methods. There are only two as far as I can see. If you switch between them then you are using the other method surely, and not a third.
I don't fly gliders but I would think they are effectively using a component of gravity as thrust. Or maybe the pilot repeatedly breathes in deeply and then blows out to one side!