This book is worth buying simply due to the fact that it's so cheap. It isn't the best of books on Greek grammar, but it does manage to get a lot of important information in. Obviously, when you're dealing with a subject as irregular and complicated as Greek grammar, you can't expect too much from a book of its size, so it's surprising to find there's actually quite a lot in there. If you're new to the language, or you need a small book to carry with you for reference then this will serve its purpose well. If you're wanting a more detailed grammar, I'd recommend 'Greek: An Essential Grammar Of The Modern Language' by David Holton et al.
A word of warning- this book was written in a time when a different accent system was used in Greek. The language hasn't changed but accents have been greatly simplified since then.