I haven't used books 1 - 5 but I found the Maths dictionary invaluable.
Would definetely recommend it.
Totally agree about the Math Dictionary. I believe all the books and sections are important . My dd has covered all. However its quite heavy and time consuming so I suggest you make sure she knows atleast 5 questions from each section on each page . If the child masters them they know it if not go over teaching and try some more questions on those pages.
I peronally find Maths watch a great back up for teaching and explaining all areas in maths!
What age is your child or school year more to the point?