Installation: 

Addon should be installed by clicking the .zip file when installing it in Blender. If you install it unziped, it won't register as an AddOn. 

Preferences:

There are Addon Preferences that allow you to toggle the display of buttons in the 3D Viewport Header, and to toggle on or off the keymaps that conflict with the AddOn.

The "Add Button to 3D Viewport Header?" option will toggle on or off the display of two icon button options that display the Orbit Method currently used. The buttons also change the Orbit Method when clicked.

The "Toggle Conflicting Keymaps?" option will toggle the keymaps in Blender that conflict with the " ` " (a.k.a. "ACCENT GRAVE") keymap created by the Addon to toggle the Orbit Method in the 3D Viewport.