^Back at the Crosstown Open Doors event, they had the door apparatus for one of their Flexities open and on view.
I'm not an engineer, but this just looked.....flimsy.
Of course, the belts in my car motor certainly hold up well, so I suppose these would also.
I'm surprised it isn't linear magnetic drive (vs belts). But maybe due to speed (at least my experience with linear magnetic doors has been that they take slightly longer but it may have just been the magnets used)