Biz,
IMHO I wouldn't bother with them unless you really like spending money. When you do your various courses you should get a text book supplied by the school/company and your class notes should be enough.
Sometimes however, I needed another "view" of the subject so I acquired a text book. I view these books as something I will be referring to long after the course has finished. (and indeed I have done so over the years) I was supplied with the 4 forces textbooks for my JAR ATPL and I didn't think much of them.