I used a voice recorder in API. Nobody had any problem with it. I would just say something to the instructor before hand to be polite but he/she shouldn't have a problem with it. It actually helped.
Usually the instructors will give a review right before the test which usually focuses on exactly wht will be on the test. Having it on tape was cool cause I could play him asking the question, pause, answer and then listen to the answer. Also, sometimes the instructor would explain something (that I didn't understand when I read about it) a certain way so that I could understand it. Having that on tape and then reading the book helped a lot.
Yeah my boyz joked about it, like I was too serious or something but hey ... it helped me and no one is gonna knock you for trying. Do what helps you.
Peace,
-Spin