An integrated shield visor is a transparent or tinted face shield built right into the helmet—think of it like a motorcycle visor but lighter. It completely replaces your sunglasses, which is great if you find regular cycling glasses uncomfortable or if you switch between prescription glasses and sunglasses constantly.
The big advantage is aerodynamics. On aero road, time trial, and triathlon helmets, an integrated shield creates a seamless airflow over your face that separate sunglasses can't match. Commuters also like them for weather protection in rain and wind.
The main downside is fogging—these shields can fog up in humid or cool conditions since they sit close to your face. They also add cost to the helmet and can be expensive to replace if scratched. If you mostly ride in hot, humid conditions or prefer the flexibility of swapping between different sunglasses, you're probably better off with a standard no-visor helmet and your favorite cycling shades.