Personally i wouldn't bother with paying for books or online courses for this one. I went through the AC 61-7 which tells you what you need to know and used the rule parts which are accessible on the caa website to get the answers. If took me 2 weeks of about 4-5 hours of study most days to get through it and passed well.
As a general caution with all asl exams the acronym RTFQ ( read the fu@ken question)
works well.