Buy it! If you have any interest at all in how your guitar amplifier works, you need this book - I can't recommend it anymore than that! Dave has authored more books from Publisher Backbeat Books, and they're all killer productions - great/informative writing, superb binding, covers and great detail in the publishing aspects of these books.
Dave Hunter is well versed in all things guitar, as I have learned through buying and reading all of his works to date. He's got a unique book here in his approach and honesty on the subject, and it's worth every penny. Loaded with real world, no BS information - great sections on signal chain, components, how to select the right amp for you and at the end, a fully documented amplifier kit (which is now available through the publisher's website) which you can either buy direct, or put together with your own parts!
Highly recommended, and I highly recommend Dave's other books as well!