When crouching you cannot move when using the shield cause you are 100% protected then. When standing the shield covers you from head to knees. The shield is really heavy so you are going to walk very slow when using it. Almost all bullets are stopped by this shield. The shield has a small opening trough which you can look. This window is very small so you will have a limited view.
Furthermore the shield has a flashlight mounted on it so that you can see in the dark. Not 100% sure but probably you can also use a sidearm when using this shield.