I normally wear mine on long trips in conjunction with my under jersey protector.
Researchers claim that it reduce in 30% the chance of neck injuries ( not eliminate).
When its too hot i wear only the under jersey protector without the jacket.
The alpinestars Bionic Pro model has straps build into the under jersey protector for better attachment.
With this configuration, the rear support goes over the back protector, in a recessed area, eliminating the possibility that the neck brace protector rear support will brake your back (that's an strange argument used on the second video).
See in the pictures below: