Are Add-Ons per installation or per company?

Most add-ons can be turned on and off through Tools -> Add-Ons without requiring activating a unique activation code. 

If you do receive an activation code for an add-on, the code will activate the add-on for all companies within your NolaPro installation. The same is true for any add-on that is turned on. The add-on capabilities will be available for all companies in the installation.