Please rest assured. We never store your data on our servers, and the app does not send your data anywhere except to the services you choose to use.
Your data is saved only on your device, except in the following cases.
When you use the Google Drive backup feature, data is sent to and from your own Google Drive. When "Link Google Calendar" is turned on, events you save to a Google calendar are stored in your own Google Account. We hope this puts your mind at ease.