Just uses the "Usage Data" that is already inside most of the modern smartphones. LOL and simply adding a simple GUI with a firewall and even though you need to pay some dollar/s per year to use the added firewall, not really worth it since, I think, only a few system apps were able to be disabled through its firewall. However, the only things that were usable here was the realtime use of data of your bloatware apps. Notification for apps using some data only functioned once then is unusable...?