Wow in that photo it looks like they're going for clockwise rotation, to rotate the maxilla down???

I think it sounds like it would cause the lower jaw / chin to not be able to grow forward and give a receded look. I haven't seen what Mike Mew uses, but theres another alternative "The Bow" which has one point on the forehead and the other on the chest, which again frees the lower jaw.

The way I see it, pretty much all craniofacial issues never result in the forward positioning of the midface too much relative to the forehead.  In other words, even if one were to inadvertently retrude the forehead while having the benefit of moving the midface forward, it's worth the cost to virtually anyone willing to use the facemask.

The chin is another story; those of us who have a relatively protruding chin would pretty much all agree that moving the midface forward at the expense of potentially retruding the chin, is also worth it.  Those with a retruded chin may want to at least consider alternatives to the facemask.

Your chin might be forced back a bit due to the backward force on it and the tmj condyle jamming up against the socket.  But trust me your forehead is unlikely to change.   The frontal bone is very very stable except for maybe the frontal sinuses (so-called brow bones).    

I agree with the OP. The force is going to get transferred somewhere. I'd rather hook on to a big rubber band on something free standing than use a facemask.

Bumping as I'm going to start wearing a face mask soon.