I've had this book for a little while now, but it (sadly) hasn't really helped very much. This is a shame, as for a reference grammar it has a lot going for it - plenty of examples, enough exercises to get to grips with the language, and explanations that really aren't bad at all.
No, the big problem is the lack of Chinese characters. There is a wide variety of vocabulary used, and literal translations are not always given - leaving the student floundering, having to look up each word, when the inclusion of the characters would make the task infinitely easier for anyone who knew them.
In any case, it's not like it's difficult to learn the writings (see James Heisig's books), and when learnt, all of Chinese falls nicely into place. You can feasibly understand anything written in just a few months, and excluding them means that literacy is that much further away from all students. Yes, Cantonese is primarily a spoken language - but being able to read and write lets you build up word-power in it very quickly. Without... and you're just stringing together apparently disparate, orphaned sounds.
That said, the resources out there for learning Cantonese are few and far between, and it's not bad for getting a feel of the language - it's just disappointing that the authors decided to omit the characters, and this sadly renders the book a lot less helpful than it could have been.