What does it cost?
Watching and every explanation are free. One €4.99 purchase unlocks the rest.
Procession is free to download. Watching your Mac, every explanation and verdict, why is my Mac slow?, Show and close, and Look up are free.
One purchase (€4.99, £4.99 or $4.99, or the local equivalent) unlocks history, alerts, the menu bar extra, Review one by one and the report, on every Mac you use with the same Apple Account. No subscription.