I got Audio and Notes for BEC in order to get a jump start while traveling. There is a good amount of overlap between the two so it depends on the learner (auditory or visual or a little of both). The Notes have a bit more info on specific formulas, etc. Best bet is to get the free sample that is provided and compare.
I haven't used them to follow along with each other but to use one when I can't use the other. Both are meant for repeat reading/listening. Commute, workout – audio. Reinforcing difficult content or bringing together sections – notes.