The string (which only work in tension, so it must be tight!) doesn't appear to be of much advantage.
However, if you have an elevated heart rate, possible wobbly legs and struggling to get enough oxygen, they can make a noticeable difference to your stability.
You might not experience these symptoms if you're meandering around 500 hectares of winter wheat in East Anglia, but they start as soon as I get out of the car!
Anyway, to the real advantage of the string.
Shooting in the wind.
You will never be able to notice how effective this is until you..........try it in the wind.
Things to note:
Yes, you will have to stand still for some time when you use sticks.
The string will NOT work until you lean on the sticks and put the string in tension.
You will have to make adjustments to the strings fixed point by moving your (right for me) foot backwards and forwards.
Some people might not be able to carry out these tasks simultaneously.
Add a 150mm of soft plastic pipe to the area where you place your foot, it makes getting you foot in much easier.
I also employ the use of my sling when on the sticks, this seems to dampen down all movement.
If you can't get the hang of the string, buy a fifth leg, just as good, but works in compression.