Use local SIMs while traveling to avoid roaming charges.
Some custom firmware versions allow you to "force" 4G-only mode for more stable connections. Methods to Unlock the ZTE MF920U Zte Mf920u Unlock Firmware
If your device is hard-locked or the IMEI method is unavailable, software tools can modify the internal firmware. MF920U Quick Start Guide - FCC Report Use local SIMs while traveling to avoid roaming charges