Official Guide 12 Is it worth?

I just glanced through the OG12 at LandMark and practically saw the same problems as the ones in OG 11, especially in Quant. It's probably not worth purchasing the OG12 if you have the Orange book.

I would say that about 60-65% is old content and the format/layout/etc. has not changed. Entire sections are complete copy and paste. There really aren't any new type of questions that I have seen.

The 12th edition, in which approximately 2/3 of the questions are identical to those in the 11th edition, remains what GMAC has always intended it to be – a resource of official, retired questions for potential test-takers to use as part of their preparation regimen.
I would suggest to finish OG11 comfortably with high accuracy then go ahead with OG 12.