Pros compared to build-in Blender retopo overlay: 

• This tool allows for clearer visualization of how your retopo mesh interacts with your high-poly model. You can easily identify which areas of the retopo mesh protrude beyond the high-poly surface and which areas lie beneath it (unlike built-in retopo overlay, which obscure this information) 
• customizable: faces overlay color, opacity, 
• supports drawing in: Sculpt, Edit, Paint, Object modes 
• option draw with-or without modifiers applied