The Tangle Library iOS app does not collect any data on users. If this ever changes, I'll be sure to update this page and put a notification in the app. If you're looking for explicit details:
While I'm not collecting anything right now, there are a few compelling reasons to track app usage; analytics can help track what features are being used (so I can improve them), and monitor for crashes/bugs (so I can fix and prevent them). If I choose to add any of these tools to the app in the future, this policy will change.