I borrowed it from the library. I found it to be an 'ok' book but not spectacular. I would say if you can get it on an interlibrary loan or something like that, do it. I wouldn't buy it though. I haven't found a much better book, but that's not saying much - this field is pretty sparse. My best education has been finding mic schematics on the internet, and building stuff. You learn what works, what doesn't, and you get an idea of why things are done a certain way. Start with the amplifiers - use an existing capsule. If you are really ambitious, attack the capsule. Reading (or trying to read) microphone patents is also good. Search out this forum for all of that and absorb it all. Re-read it. Print out some to read while you are in the bathroom.
The book 'Neumann: The Microphone Company' is supposed to be quite good. It has some good photos, I'd like to order it.