John Voorhees, on Moment’s app usage feature:

There are no public APIs for tracking app use on an iOS device, so Moment reminds you every morning to go to the Battery screen in the iOS Settings app and take a screenshot of the number of minutes you used each app. Moment reads the time each app was used from the screenshot using optical character recognition. If you use more apps than fit in the screenshot, you won’t get data on the ones that don’t fit, but in my experience, there was space to fit about a dozen apps, which covered my most heavily used apps.

It’s unfortunate that developers have to resort to these types of solutions, but it’s definitely a clever workaround.