I bought all 3 OG 11
books a couple weeks ago. If I could do it over again, I would have only purchased the main OG 11
book. I think the 2 separate review guides are unnecessary from a "review" standpoint. However, if you need more problems, they obviously have more available than just the main book so it's really up to you; do you need a "review" or do you need more problems? BTW - I have noticed overlap between the OG 11
and 10th editions. The added benefit to the 11th edition is that the explanations and format are a lot better (especially in V) than in the 10th edition. I love their explanations for CR and RC the best!
The format goes something like this (for CR):
<b>Situation:</b> Since the wholesale price of raw cotton has fallen significantly, the retail price of cotton clothing in stores will inevitably fall.
<b>Reasoning:</b> What point weakens this argument? Consider carefully the difference between the two products for which costs are being compared: cotton and cloth. This argument assumes that lower wholesale prices for a raw product must necessarily result in lower retail prices for a processed product...
<b>A - Correct.</b> This statement properly identifies a weakness in the argument.
B - The statement is out of scope.
C - The author's conclusion is not based on this assumption.
D - This actually strengthens the author's argument.
E - The argument has already taken this statement into account and it is not weakened by this statement.
As you can tell, the format is 10x better than the format in the 10th edition. I now understand the reasoning behind CR and RC questions a lot better.
Ultimately I didn't mind the purchase though because I bought all 3 books on the Manhattan GMAT
site for ~$50. Not sure how much that total will change with shipping to India though.
Hope this helps!