The biggest selling point of this add-on is that it allows you to edit with left-right symmetry without using any Mirror Modifiers at all.
The Pitfall of the Mirror Modifier: When readjusting a model after UV unwrapping and texture creation, using the Mirror Modifier requires deleting half of the mesh. However, doing so erases the UVs on the opposite side that you took the time to arrange neatly, resulting in a frustrating backtrack where you have to readjust the UVs all over again.

Limitations of Blender's Standard Symmetry Editing: Blender's standard symmetry feature supports operations such as moving vertices, but it does not support edits that involve adding new subdivisions (topology changes) using tools like the Knife tool.


This add-on replaces some standard editing tools—such as the “Mirror Knife” feature—with specialized mirror-compatible tools to enable symmetrical editing.
Since there’s no need to split the mesh in half, it enables a safe and stress-free workflow that allows you to “cut and adjust the shape of both sides simultaneously while preserving the existing UV data.”

(Ctrl+R) and Knife (K)—will be replaced with symmetrical tools.