The Pro version of Streakster is a paid subscription, or one time purchase (called Lifetime), that includes access to premium features such as: unlimited habit creation, iCloud backup syncing, note taking, vacation mode, no ads, a security passcode, and more.
The pricing plans for Streakster Pro in your country can be seen on the subscription screen, which you can access at any time by tapping the Pro icon (the crown) in the bottom navigation bar.