The full face tempered glass is a reinforced full-coverage glass specifically designed to protect your mobile phone screen from scratches and other damages. In case of a fall, it provides additional protection, although it does not guarantee that the screen will not crack. It does not affect the functionality of the screen.
It is 9D, meaning it has undergone special processing to have curved edges that cover the entire surface of the screen. This way, it is not obvious that the screen has protection, while also safeguarding the curved edges.