For most of our products we do allow to either license all active users or only the subset of users that requires to use our solutions. This comes with certain limitations in functionality where usage of our Addon cannot be related back to a specific user.
This blog article explains the limitations and considerations you need to be aware of when purchasing a "per User" license.
ActivityTools, SmartBar, PowerSearch: (Elements embedded into Entity - forms)
More information about how to activate per User Licensing in Dynamics 365 can be found in this blog article.