Never flash a firmware labeled "IMEI Repair + Unlock" unless you understand the legal implications of changing IMEI numbers. In many countries, altering an IMEI is a criminal offense. Legitimate unlock firmware should only remove the SIM lock, not change the device identity.
For example, on a new generic B21 firmware, users report a 30% increase in download speed when switching from Telstra’s locked firmware to an open one. zte mf283u unlock firmware new