I used to purchase more than 10 courses on Udemy, but some of the content are really bad, which ended up I need to refund it. However, they are really a few great Udemy courses on programming too, with such a low price, you can enrol into a course with lecturer support in Q&A section.
Another issue with Udemy is that some courses are shared on torrent site, which make the content creator life even harder.
RE: The Dirty Secret about Udemy