If there was one sole reason to buy this book, it would be for the extensive diagrams detailing the cheaper ways of making the more expensive retail equipment - it wouldn't be as a guide for hydroponics on its own, as the growing techniques only tend to cover one specific way of doing things, leaving little or no room for tutored experimentation.
Having said this, however, it is good for familiarising yourself with hydroponics terms and getting the theory behind everything down to a fine art - but for anything beyond setting up equipment, such as system experimentation, you need something a lot more detailed on the potentially complex setups involved and the myriad ways to produce on hydro systems.