If you look at amazon.com you'll see it has 37 customer reviews (at the time of writing this) with an average rating of 4 out of 5, so it must be pretty good
The problem with these kinds of reviews is that they are generally written by people just learning the language, and therefore cannot truly comment on the quality of the book. It could be completely wrong and they wouldn't know the difference.
Your best bet is to read the PHP manual. It's 100% free, complete, and accurate.