Simple and sturdy. There is sufficient space under the watch to slide in a screwdriver to counteract the twisting force of the opener.
The holder opens out to about 34mm clear between pins, and 27mm clear laterally. If your watch is bigger than this, I guess you could try removing 2 pins - you need only 2 diagonally opposite pins to provide resistance to the opening twist, although the watch will not be as steady then.
The pins slide in, not screw, so I keep it in the small cardboard box it arrived in to avoid losing the pins in my toolbox.