Working with multiple materials, will it add value?

My opinion is that it depends on when you do the problems from each. I started with PR materials then went to Kaplan, Veritas and finally OG materials. Once I had started working the OG problems and became familiar with the way the test writers "think" I definitely 100% noticed a difference between OG verbal and all other verbal materials. This was particularly the case with the 1000 series questions.

To answer your question, I think it is actually dangerous to use certain materials after the OG because once you become familiar with OG, you should notice your mind shifting to "think" like a test writer, but some other materials have the opposite effect. I avoided the 1000 materials like the plague after I realized this.