Modern ballistic helmets, like MICH and ACH, which are used by the Military are designed with Kevlar inserts, which are rated to stop pistol calibers. Most ballistic helmets also have an NIJ level IIIA rating at best, which is rated to stop most common pistol calibers up to a .44 Magnum.
Ballistic Visors, which are designed to act as a face shield can also have a level IIIA rating at max. Generally, tampered bulletproof glass can stop heavier calibers, however, in a small setup, like a ballistic helmet visor, it offers level IIIA protection at max. This means that it can stop multiple pistol rounds but won’t do much to stop any rifle threats.
Ballistic visors also provide protection against shrapnel and bullet fragments. It also keeps dust and other debris out of the wearer’s face and can protect against blunt force attacks as well. This is why tactical helmet visors and riot shields are more commonly used by riot control units and prison guards. They are also used in limited applications by militaries and police officers as well.