Free app for tracking data usage per app I have a user that I want to monitor as he has a specific app which downloads a lot of updates. However the user will not pay for apps and its difficult to procure it over official channels.

Ergo i'm looking for a free app that can do this. I was surprised by how difficult it was to find one in the App Store, especially when this level of granularity is native on Android and can be tracked over custom time periods.

I dont believe the Cellular Data setting

Does anyone have any recommendations?
iOS sandboxing prevents apps from getting access to data usage of other apps. That's why iOS has the Data Usage section in Settings to show exactly that. 

There might be solutions for jailbroken phones, but given your constraints a jailbreak doesn't seem to be an option.

PS: If you don't trust the numbers in Data Usage, why would you trust those in a 3rd party app?