In the course, you can presell / funnel members to your own paid products on your own site.
I'm actually thinking about putting up a free course on Udemy.. I can't recall where I heard it, but if you release a free course and are able to drive enough members/traffic to it, they'll feature it. In the course, you can presell / funnel members to your own paid products on your own site. I think a few have done this with a lot of success. I need to research it more.