MGMAT quant and SC are awesome. However both these materials are extremely saturated with content and almost all of the information is important, therefore it is easy to skip some information or forget it therefore i am going through these review books over and over again and that is helping me to get better with every revision. The Advanced questions given in the second half of each strategy guide are more than enough to get you through a majority of the
OG problems however i found the advanced quant book necessary in learning correct strategy for DS that i couldn't extrapolate from the DS strategies given in the guide books.
I would say that these guide books cover EVERYTHING that i have encountered in the
OG's or other GMAT related questions (Kaplan sources,
MGMAT sources, princeton sources, GMAT PREP etc). However you will be well served by going over strategies in the
OG material for (answers ) finding what is the best strategy to tackle a problem in under 2 minutes.
What the
MGMAT doesnt provide you with are practice questions. For that
OG (12 and 13) is the best followed by
MGMAT advanced quant, Kaplan 800, and GMAT CLUB forum questions (bunnuels pdf etc). For a 90+ percentile prep
GMAT CLUB tests are the absolute best !!