A lot of these books are of limited value without a competent instructor to help you along. They can be very wordy (like PoF), and as little as 5 - 10% of the actual content is directly relevant to the exams. Whilst it makes interesting reading, provided you don't lose the will to live too easily, unless you have lots of time on your hands then you run the risk of trying to absorb irrelevant information. The instructor will sort the wheat from the considerable amounts of chaff.
Performance is slightly different, in that the manual is very short, and the subject is perhaps more 'practical' in nature as there is a lot of calculation from performance charts involved. A decent instructor is worth his weight in gold for this subject, as it is one of the few you will ever have any use for once you graduate.