The short version, until the long version is written.
An SSA Pro license covers one or three WordPress sites for one year of updates and support (or month by month, if you choose monthly billing).
If Pro is not for you, ask for a refund within 30 days of purchase and you get it.
When a license expires, Pro keeps working. Updates and support stop until you renew. Your data is never held hostage.
The plugin and the add-on are GPL-2.0-or-later software.
Questions about any of this? Email [email protected].