How to install this addon ?

in preference / Addons, install the zip file without unsipping it

Check the box near the name of the plugins

Close the window. The addon is already installer. You will fin it in the 3D viewport, in the Sidebar (N key)

How to use this addon ?

Select objects you want to smooth

- Apply Shade Smooth on selected objects (A selected all objects if you need).

(If Autosmooth button is checked, same value of Autosmooth will be apply on all selected objects !)

- Apply Flat Shade on selected objects

- Add a Subdivision Surface Modifier on selected objects base on Viewport and Render choices.

- Delete Subdivision Surface Modifiers on selected objects