You can download it for free on the App Store, and it has an option for a $3.99 pro upgrade. The upgrade unlocks features like:
- Unlimited Habits: Increased from five in the free version.
- Habit Stats: Current streak, best streak, and other stats for each habit.
- Week by Week: A progress indicator showing how successful you were at completing your habits each week.
- Passcode Lock: Track habits in private.
- Better Reminders: Set time-based reminders for each habit. The free version only supports reminders using generalized times of day (morning, afternoon, evening).
- Floodlight: A lighter theme.
You can read the entire review over at The Sweet Setup.