I used this book to revise for both A+ exams (Hardware and O/S), and found it very helpful in my preparation for the exams. It is a great book if you already know the basics and have some experience of PCs.
It is great because it goes straight to the point, however if you are looking for a more in depth coverage of specific topic, you should look for example to Minassi's "complete PC upgrade and maintenance guide" or other A+ books.
So, in conclusion, a book to read in the last stage of your studies for the A+ exams, to make sure you have covered all the exam's objectives.