My complaints about DataMan Pro are few, and the most major of them may be more of an issue with iOS: Even when Background App Refresh is enabled, the app sometimes still seems to get shunted into its "frozen" state and I don't end up getting notifications as I expect. But relaunching the app fixes that, and the figures within the app seem to remain correct. I also find the interface, which is largely gesture-based, a bit opaque at times: You have to swipe up on the screen to get the app or day breakdowns, and swipe left to get access to preferences and settings, hardly the most discoverable methods — an indicator à la the one Apple uses for Control Center or Notification Center on iOS 7's lock screen would help.
If you're not quite ready to pony up the $5 for DataMan Pro, you can also get many of its features in the free DataMan Next. But you won't be able to break down your data usage by location or app, the notifications are in-app only, and the forecasting feature isn't quite as smart as DataMan Pro's. There's also a $10 DataMan Enterprise that adds the ability to track multiple data plans, automatically export statistics, and more.
Still, if you find yourself getting regularly smacked with overage charges, or just want to know how much data your apps consume, the $5 cost of DataMan Pro isn't too much for a little peace of mind.
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