Are you talking about the book First Aid for the USMLE Step I? If so, then absolutely, that book is amazing. Stay away from the First Aid for the NBDE Part I book - that one is garbage in my opinion, it's nothing but a listing of information akin to the dental decks, no mnemonics or anything. The USMLE first aid book is amazing though, TONS of mnemonics. Use it for micro at the very least, and biochem (or more) if you have the time. I'd shy away from all the pages on drugs in the micro section though, since it gets a little too deep and wouldn't be nearly as high yield as studying the other stuff.