It employs new NetworkStats package and reads data directly from your device. Hence it does not run any background process and will not consume additional CPU power.

On first page you can view data usage in current billing period.

On second page you can review usage history on daily weekly or monthly basis.

With simple setup it is ready to use.

Permissions required:
READ_PHONE_STATE
It is used to read SIM info to retrieving mobile data usage.

ACCESS_USAGE
It is used to retrieve usage history.

Note:
This app only runs on device from API 23 (Marshmallow) onwards.