The idea of the right angle finder is as old as the hills. Cartier-Bresson, Helen Levitt and many other early street shooters used them. It is a small device that is attached to the viewfinder and allows you to point the camera in one direction while you appear to be looking in a different direction. You can still buy them for most modern SLR cameras. I have one for the Canon SLR I use.
In some ways, it is similar to the flip out LCD on high end point and shoots; or even the way you look down at a ground glass with a camera like the old Rollei Twin Lens. Even if you simply use it to look down at the image, rather than anything fancy like turning it so your camera is pointing off to the left or right, it makes a very big difference in how you are perceived by subjects. The idea that you are not directly looking at them, even though the camera is – well, as I say you would be surprised at the difference it makes.
Bresson actually had a right-angle finder for his Leica which also inverted the image. Rather than being a handicap, it’s useful to be able to look at an image flipped left to right or even upside down, as with the ground glass on a view camera. It abstracts the composition in a way that makes is easier to see than if you are looking at the scene straight-on.
Modern right-angle finders don’t flip the image – but as I say – it wouldn’t be the worst thing in the world if they did.