The user settings stored are those needed for use in the app, including:
These settings are managed in the settings screen of the app.
Notifications to update the number of days left on the app's badge are driven via Google's Firebase service, which will send and store a device identifier to enable this functionality. Please refer to Firebase's terms of service for details.
The app also will show ads from Google Mobile Ads, unless the user buys a Pro Pack. Please refer to the Google Privacy and Terms documents for details on the information collected by this process.