I looked at their website and it seems to be very vague about what the system involves; to find out more, you have to buy a course. If it hadn't been for Merlin Mann's free blog, I would probably never have plunked down my $12 for a copy of David Allen's
Getting Things Done: Merlin's posts told me enough about GTD to make me decide it was worthwhile.
After a bit more googling around I found a couple useful articles
here and
here.
On skimming them, it seems that the advantage of Mission Control over GTD is that it encourages you to think more about overall time commitments: what is possible to do in the time you have available and what your relative priorities are. I can see the virtues of both of those. I don't think I need the granularity that Mission Control emphasizes (or appears to emphasize, based on those summaries), but I can see how it might be very useful to some people. Personally, I try to allocate a certain proportion of my time to each of my areas of responsibility, and to focus on those on certain days and times (sometimes with OmniFocus's Focus command, sometimes less rigidly), while recognizing that emergencies and seasonal rhythms might change my allocation. (Example: I'm a college professor, and my balance between teaching, administration, and research shifts dramatically during the summer.)
Since you have investigated Mission Control more deeply than I have, could you let me (and the rest of the forum's readers) know whether there are additional emphases of the Mission Control approach, and whether you think the courses are worth the US $150-300 that the online courses cost?