Leitz Leicaflex - very SLR - Single lens reflex camera (SLR)

Leicaflex camera in a very special and unusual version.
The camera has no built-in light meter and is fully mechanical
The shutter works fine.
Under the viewfinder you can indeed see the row of shutter speeds.
What the function or meaning is of the piece of covering under the prism is not clear.
The text at the bottom raises more questions:

"The only 100% mechanical Leicaflex first batch in the world"