For how this works, check out Ghost Blind, you can see pictures and videos of it in action. Basically you create an illusion of a mirror, which shows the viewer a random segment of the opposite wall, or the floor or similar. So long as the wall is amorphous, it is bloody hard to see, especially since the mirror can be curved and will be dirt and dent free. That said, positioning is key, and if the floor is a very different material than the walls, it is almost impossible to use (could maybe do it in a corner).