On a trip to China I ordered this phrasebook as I have absolutely no knowledge of Mandarin and was told China was quite difficult to get around in due to the low level of English spoken over there.
In truth, at places like airports staff there will speak English and signs will be written in English. In Beijing airport I was even able to ask a janitor a question in English and he understood me. In more rural China (specifically I went to Fujian province) it's very unlikely that you'll come across someone that can speak English, but places still have some signs in English.
Following on from my previous point, the writing system will pose a problem and is one this book cannot solve, not that it aims to. Rather you will just have to be adventurous and hope for the best. Restaurant menus are a good example. If you're not the adventurous type or you don't fancy risking it in a restaurant, don't rely on this book for getting around.
When it comes to speaking, however, this book does a fairly good job when taken into consideration how hard Mandarin pronunciation is for beginners. The phonetic pronunciation in the book is not too far off the correct pronunciation and if you do get misunderstood (which will happen) you can just point at the Chinese version of the phrase/word.
One problem the book has which I would not have known about is that the phrases and translations given are not exact. I had a Chinese native translator with me who told me the book was 'not very good'. Apparently the translations provided for each phrase in English/Chinese are not particularly accurate and could be misinterpreted.
Overall, it's a handy book to take with you and a starting point for people with no knowledge of the language. Thanks to the uniform writing system, it's good in Hong Kong too as you can still point at the Chinese!