The screw in most vises has a thread length at least equal to the maximum jaw opening. It threads into a fixed nut and provides continuous jaw movement. The screw thread in these vises is quite short, threads into an adjustable nut and provides discontinuous jaw movement of only half an inch or so per setting. User satisfaction in use is highly dependant on how quickly, easily and positively the nut can be moved from one position to another.
I found the action of the stock vise quite frustrating. Moving the nut from one position to the next seemed to be just one false move after another. Since its position is hidden by the vise base and workpiece, I was always working blind. Push, pull, turn one way or the other and finally get it into a notch, maybe, and often the wrong one. That’s probably an exaggeration but it’s the way I remember it.
The cause of all this is the nut itself as shown at the right. It doesn’t fit properly in the slot and as soon as its pins clear the notches, further turning of the screw twists them out of alignment. Getting them aligned again seems to involve as much luck as skill.