If you already understand the topics to the level required for the MCAT, that strategy could work, but there are a few problems.
You do not know if you know the information well enough unless you go through the study materials and see how deeply you need to know the material. I got A's in all of my prereq's, but there were still some things I needed to work on because they were either skipped or barely covered in my classes. For example, my physics class did not cover fluids, light, or sound.
If you don't know the material well enough, you won't understand the explanation as to why the correct answer is correct. The question will thus be nothing more than a note to study that topic rather than an exercise in applying your knowledge to an MCAT question.
The test prep books have strategies to save time. They teach you to solve problems quickly without a calculator. Classroom physics exams are nothing like MCAT physics problems. You should use a guide to make the transition to the MCAT style of testing. I highly recommend the Berkeley Review books for this(except biology, that book is silly dense). Their shortcut formulas can help a lot on the MCAT rather than using the more accurate, but much slower, classroom formulas.
Even if you did have the knowledge to do well on the MCAT, lacking the strategies that were developed over years and that most of your competitors will be using will leave you with a far lower score than you could have gotten if you studied properly.
I used a modified version of the S2NED method(less practice tests, more studying) and landed a 35, but YMMV