The advantage of a tang sight vs replacing the rear sight with a peep is two fold. First, you increase the sight radius from about 20" to 30" using the tang sight. Second, and just as important if not more, the tang sight is up close to your eye and as such, you can use a smaller (.042") target aperture that isn't practical in a peep rear sight as the aperture is too far from your eye to use. The small, target aperture up close gives the added benefit of increasing the Depth of Field (DoF) which an aperture rear sight does not as it's too far from your eye.
Increased DoF means that, surprising as it may seem, you can see both the front sight and the target, even though it's far away, in great focus. That's because the optical principle of DoF means that decreasing the aperture you sight through close to your eye increases the DoF, i.e. the distance from your eye that all objects are in focus. Even if your need bifocals or progressive lens to see well (I do), the increased DoF gained from sighting through a .042" aperture close to your eye is amazing. Further, the target aperture gives a smaller sighting circle for finer sighting.
Longer sight radius, smaller sighting circle for finer sighting, and increased DoF so that the front sight and target are clear no matter the range. The tang sight with a target aperture is a wonderful addition to your rifle, no matter the style.
