The
MGMAT books are very good as a review of the fundamentals, and some of the questions are actually quite challenging unlike the fare you will find in the kaplan gre/gmat math book for instance.
Unless you are feeling rich (or are rich

), I would just buy the ones for areas you feel particulary weak in and use other sources to brush up on the rest. You won't find any holy grail tips in them that you wont find elsewhere (except perhaps for the
MGMAT SC book, which doesn't really have any equivalents), but they are an excellent way of building your knowledge from the bottom up.
I can also highly recommend this book as an additional source of tough questions:
https://www.amazon.com/Turbocharge-Your- ... 0978843509
It is not the same company as
MGMAT, it is Manhattan Review, I have both the Verbal and Math M Review books. The Verbal is something else in terms of difficulty, I am reasonably competent in V and this book blows me away, however the Math book, though challenging, is alot more realistic.