The full face tempered glass by Hofi is a full coverage hardened glass, specially designed to protect your phone's screen from scratches and other damage. In case of a phone drop, it does not guarantee that the screen will not break along with it, however, it is an additional protection. It does not affect the screen's functionality. It is 3D, which means it has undergone special processing to acquire curved edges that will cover the entire surface of the phone screen. This way it is not apparent that the screen has protection, but additionally, the curved edges are also protected. It is compatible with Galaxy M21.