In summary, the NECG sight in factory form is about as good as it can get.
There are issues with leaving out the aperture on the NECG sight. First, the elevation slide is not a tight fit in its slot. The aperture actually locks the slide against the sight body to keep it from moving around. Without the aperture, it will move. Second, with the aperture removed, the resulting "hole" is not round. The body of the sight protrudes into the hole from both sides where the aperture contacts the body to lock the slide. It is like a circle that is partially truncated on both sides, leaving a hole that is taller than it is wide. These issues may not bother some folks, but they bother me. The movement of the elevation slide is not a real issue at close range, but as range increases the problem is amplified.
