If I understand the mechanism here, it looks like the vise part is really just engaging the worm screw and keeping it still. That said, I've never needed to worry about my adjustable wrench worm screw that much. Maybe the tolerances are extra sloppy and that somehow makes it cheaper to manufacture and the vise bits are just extra shit they are trying to get rid of? With a proper adjustable wrench with good tolerances, there isn't enough slop in the worm screw to justify this mechanical nonsense.