I have found McKeown's book to be a very interesting way to have an idea of what is out there that one may not have heard of before.
It seems to have odd gaps with some makes getting far, far more coverage than others (especially in 35mm) with the Aero Technika being totally missing.
It is called a guide to antique and classic cameras, which I imagine could be used as a reason to exclude, but then for heavens sake can the "toy" section.
I am sure there are other gaps, but it is still, as far as I know, the only book out there that even comes close to showing more than a fraction of what was once available.
I would say that a good soft-cover volume is not money wasted.