Installation of the plugin:
Open Blender --> Edit --> Preferences --> Add-ons --> Install --> Navigate to where you've downloaded the Plugin in (hit Install Addon) --> it should pop up in your add-on window with it enabled (if not enable it). Now you should be able to see the Addon in the viewport.

HOW TO USE:
Select any animated root object that has keyframes and hit Calculate Speed.

Known limitations:
Sometimes it generates a result of Zero. This is due to the object's relationship being a bit more complicated than one can anticipate. 
 - The quick solution is to manually bake the animation of the object until you can see visible keyframes on the timeline when this object is selected.