The kaplan courses are usually too time-intensive to be helpful for usmle prep, as are the online videos, unless you need that type of thing. Free Qbank and books would be nice!
My brother taught SAT for Kaplan and liked it well enough, great pay. MCAT prep pays well but they demand A LOT. His friend did that and apparently had to prep for hours before the class and was routinely scolded for not being "prepared enough." I guess with what they charge for the classes, the teachers have to be, but he really was prepping, it just semeed to be a scare tactic. He said the students were somewhat high strung as well. LOL. He wasn't premed, he was physics, and taught that section for the MCAT.
Overall, it seems like a good way to make some good money.