Which YouTube video? An example of one person surviving doesn’t mean everyone does. There are also the obvious considerations such as impact surface, angle, etc.

The DG website states that :

“Since there is no crush zone in a glider as there is in an auto, a crash at higher velocities – mostly over 60 knots – is not survivable. In actual crash tests at “only” 30 knots and only directly on the nose, high loadings were measured with dire results for the pilot.”

I’m certain DG has added that headrest as part of the design of their sailplane - which is a certified aircraft. Removing it without proper authority may not be legal (or smart).

Nick