It's a good book for beginners, but I'd advise you to at least know how to read the thai alphabet before reading this.
To me it was a starting point to get the most common things before I tried other (a little more complex) thai grammars.
The biggest flaw in this book is using only phonetics to teach words in thai, like, this does not make any sense, man, I NEED to learn how to read it to so I can make the connection between phonemes and the corresponding written letters.
Some more specific aspects of thai language are also under-explained (and I've figured that out the hard way), but like I said, if you want to start learning thai then you must learn how to read the alphabet and then go and read this book it'll help for sure (I'd also suggest for you to write the written word were the book uses only the phonetic version, it'll help a lot)