YMMV with results from how you use these materials. I used UWorld earlier on, because it allowed me to adapt to how actual MCAT questions are written, while also serving as a content review. I made sure to dive into the right & wrong answers for each question using TBR. Most importantly, if I ever thought "I'll learn that later, it isn't hard"... I learned it now. I made review sheets for each subject with tough topics/equations that I was shaky on. I got a 130 in CP on the real deal.
Like I said, YMMV. As a poster above said, using it as full-section practice is a great use as well. Either way, definitely use it. Aside from the official AAMC stuff, I thought UWorld helped me the most.