Oh, very good question.
Aside from such sources as Amazon's website (reviews found
here) and GMATClub's short
overview, I don't think that there has been any detailed post solely dedicated to a review on this product. That's a shame, since this is the only GMAT-specific guide for RC (the Powerscore RC Bible is actually an LSAT book, although there is a
review for it).
From what I gather, the
MGMAT RC book is decent, but nothing extraordinary. It doesn't seem to be on the same level as Manhattan's SC or CR guides. But since you already have the guidebook, it's definitely worth reviewing. If you find that there is too much information in this book, though, re-reading is hopefully an option. I found this strategy particularly helpful for the verbal books. Sorry I couldn't be of more assistance.