Let's start with the good stuff -- it's very concise, not overloaded with information that might distract or scare away a new singer. It covers many important areas and the advice seems generally sound. If you have already had lessons for awhile, the advice in this book is advice that your teacher should have already given you, but it's nice to have it all in one place in such an easy-to-use format.
However, it needs to be updated and references need to be included. The advice seems good, but it isn't unreasonable to expect that recommendations are evidence-based. The research is out there. Cassette recorders? Even "way back" in 2004, digital recorders were ubiquitous and cheap (not to mention ridiculously convenient); now it's almost impossible to find a cassette recorder. My phone actually makes great recordings -- ones I can email to students during their lesson. Also, lip trills are not useful because they are silly. They are, admittedly, extremely silly; but that's not the main reason they're so useful.
Those few issues aside, a person new to singing (or new to lessons), can find useful information here to guide them on their way. Hopefully the author will put in the extra work for the next edition.