You'll be pleased to know that the app is not only a one-time payment, but also has zero tracking – no analytics, no logging, no adverts, and no data collection of any kind.
Source code wouldn't help, because there's no way to verify any code I showed would be the same as the version on the App Store. Fortunately, you can just watch the network packets leaving from your device when you run the app, and you'll see literally nothing coming to me.