This is an OK book, but certainly not worth the over $800 that is being charged for it. What you get is a Xeroxed, front stapled book.
The information in it is generally good, if a bit old. It's an honest effort, and definitely worth, say, $5.00 or so.
Just to clear things up: numbers stations are not a mystery any longer. From the beginning, SWLers have been referring to them as spy stations. Well, that's exactly what they are.
When a government wats to communicate with its spies, they use numbers stations. Numbers stations are cheap to run and easy for agents to hear: even the cheapest shortwave radios can pick them up.