These 1000 documents are a collection of SCs, RCs, and CRs. The problems/passages/arguments have been taken from many different sources - OG, Kaplan
, Manhattan, GMAT PLUS and even the much dreaded LSAT!!
It is an excellent resource to practice from, especially the SC and CR sections. You guys will realize that after a bit of practice on the OG, that OG is pretty easy. You will need to practice on much tougher problems and thats exactly where the 1000 documents step in. And it is always good to practice on tougher problems, so that when you take the actual GMAT, it will be a breeze.
Further, the verbal pattern in the actual GMAT has overall been a bit tougher than OG. SC and CR are indeed much twisted and complicated than the straight forward OG ones. RC reflect the OG level. So make use of the 1000 documents!
Hope this helps!