I've used the 1911 and Glock versions. The theory behind the Vickers sight was explained to me like this:
The whole sight is tapered as it goes up (trapezoid shaped) do draw your eye to the center. As does the non-serrated portion contrasts the front sight.
The U-notch bottom allows the eye to more easily recognize if the front sight is off center in the rear notch. With a square notch, your eye does not notice as quickly minor deviations left or right by comparison. The straight walls/sides of the "U" also help with this like with traditional sights (some company's u-notch rear to not have this and are more of a "V" shape).
Mind you it's a "combat" style pistol sight, but it allows for a good deal of precision...not as much as say a thin fiber optic, but I would consider it an upgrade to the gun.
One thing I will also note is that if you're someone who likes to skip the tritium at the rear and run only a front sight with tritium on a defensive gun, I feel this style is more forgiving in allowing for that type of setup (but that may just be my perception).