I actually took an edX course, "Introduction to Aerospace Engineering: Astronautics and Human Spaceflight." The course number, 16.00x, resembles that of the regular MIT course, "16.00 Introduction to Aerospace Engineering and Design," and was taught by one of the two professors teaching 16.00.
The edX course is an "Estimated 8 weeks, 3–4 hours per week." The actual MIT in-person paid-tuition equivalent is a "2-2-2" course meaning a total time commitment of 6 hours per week (2 lecture, 2 lab, 2 outside prep) for Sept 8 - Dec. 9 = 13 weeks. So by comparison the edX course = 24-32 hours, the actual course 72 hours. Of course there is no comparison between lab hours and anything you can do at home. And having been to MIT I would say that to graduate with a decent GPA you needed to spend more than the catalog hours in outside preparation.
The quizzes and their scoring for the edX course was more or less of a joke. Much of the score is based on small number of short multiple-choice quizzes, in which a passing score is 50%, and in which you are presented with four alternatives and given
two tries at getting the right answer. It's not quite
that bad--one of the more stressful parts of the course consisted of "writing an accident report" for an aviation accident; your report is graded by three classmates, and you grade three reports of other classmates, using structured rubrics.
Still, I would guess that the content, work, and amount of education absorbed from the edX course was probably 20-25% that of the similarly-named in-person course. And because of the fairly non-rigorous grading and scoring, a "certificate of completion" of an edX course is... not much.
I've taken two other edX courses--one in three-dimensional sound (a challenge, because the course was given in Spanish) and a Harvard course in rhetoric. They were considerably inferior to 16.00x. I would certainly say that all three courses were worthwhile, and that I learned something. But I would also say that they have a small fraction--I said 20-25%--of the content of a real university course, and far less rigorous in grading.
In other words, they may make you a more valuable worker with a wider range of applicable knowledge, but they aren't "college courses" and no hiring manager is likely to view them as equivalent.
I think there are actually are some online courses with much more content and rigor that
do give you actual transferrable college course credits.
Annual income twenty pounds, annual expenditure nineteen nineteen and six, result happiness; Annual income twenty pounds, annual expenditure twenty pounds ought and six, result misery.