So far I have gone through the RC book and I can tell that it was pretty substantially rewritten. It is hard to judge if it is better or worse as different RC plans work better for different people. I would say that if you have the 5th edition and it did not help, get the 6th edition and vice versa.
On the Plus side of the RC:1. I found good examples how to take notes - that's helpful and what takeaways to jot down along with some short hand examples (it is helpful to learn short hand)
2. New exercises, passages, and examples added (not all but I would say at least 30% of practice content is new, and potentially more)
3. It seems the RC has been somewhat simplified focusing on getting the most important things right - the 80%
4. Good selection of Scope questions though there is no dedicated chapter/section on scope (perhaps I missed it?)
On the Minus Side of the RC:1. Fewer passages and questions. I found only 21 passages and 40 questions
2. The book never really stops to show a nice diagram of the RC question attack process - similarly to how SC book has it. That is the crown jewel and would be very helpful to use as a guide. I felt the book just threw me into the RC without easing into it (I felt the SC book did a better job of easing into the SC). This is a relatively minor grievance but it would be helpful to have a central reference point
3. Found some typos already (Page 18 has #6 instead of #2 and Page 23 has a different word in the answer explanation). Again, these are minor and every book out there has them so I would not fixate on this fact too much.
My takeaway: if you have 5th edition and need extra help with RC, buy the 6th edition
MGMAT RC book. It will be worth a new fresh look... esp since the RC options are meager. If you are still struggling with RC, try the Kaplan Verbal Workbook - it is much more spartan in terms of content and strategies, but perhaps that is exactly what you need - a solid basic foundation.
P.S. Keep in mind that
MGMAT has the
MGMAT Verbal Foundations book - if you are a non-native speaker, buy it as a pre-requisite. It will be the most valuable book of all for you.