It would be extremely useful if you could see historical/live data usage for devices.

Approach:-

• Gold Approach - Historical/live data usage over given periods (akin to Google's Mesh units) for all devices would be ideal. Understandably a big request as it would require cloud storage of all data usage. So a big ask!
• Silver Approach - Historical/live data usage for devices at least while the (Android/iOS) app is running would be nice. The app is clearly able to capture all data usage across all devices, so it could at least be collect and show all these values while running.
• Bronze Approach - Historical/live data usage just for a device only while viewing its details would at least be a nice useful feature.

A graph could be shown with the usage axis self scaling to the highest value shown on it, which is quite a standard way to show data these days.

eg: Something a bit like this:-

ps: I know other options can be shown in the area used for these graphs.