As someone who took the old MCAT, I wanted to just put in my 2 cents. (Maybe it's not worth much, but wanted to try to help out any way that I could.)
My breakthrough in studying was when I realized that the other material outside of AAMC material was not very representative of the test. Before then I was practicing from Princeton Review, Kaplan, etc. and I was only scoring at most 33. I began hitting 35 and 36, after I made sure I had my basics down and began only focusing on AAMC questions. In the end, no test prep company can compare to the AAMC’s question style. Thus, if Khan Academy has partnered with AAMC, I would think that doing all the problems and watching all the videos would be a very good investment of time.
Also, don’t underestimate the importance of knowing your basics inside and out. Having equations and concepts on the tip of my tongue really made the difference for me on test day.
I got a PS 12, VR 12, and BS 12, Composite 36 on the real thing.