Aren‘t those used in conjunction with a mask?

According to this article at the link - L.A. based designer Dom Vetro is making full-coverage protective face shields that fit over N95 masks in its factory in Culver City.

Designed with locally sourced materials such as high-clarity plastic to fit over medical masks including N95 types, this reusable shield (which is washable with soap and water) is sold in a kit that includes a translucent sheet of fog-free acrylic; two industrial-strength fasteners that can be attached to any pair of eyewear–optical glasses, sunglasses, goggles or safety glasses; and a specialty cleansing cloth. The full-coverage 12-by-9 inch design protects the entire face including the eyes, nose and mouth without affecting the wearer’s vision.

I does say that it's compatible with a N95 mask but it doesn't say that it's only to be used with a mask. I will research more.

No, too much open space. They are used with masks.

Same benefit as a mask? Not even close.