I have seen photos of those on websites taken from the inside looking out.
They do block visibility some but not as much as other "covers."
The SHR isn't a cover. It replaces the glass.
I had a 1966 fastback, actually two, one in the 1970s and one in the 1990s. The rear side window louvers in those provided no visibility at all. But I would love to have either once again.