@mike_orbit, your mileage may vary, but we had two of the AT&T/Verizon versions brick themselves after the upgrade.
The initial upgrade went OK, but then when the actual Quectel modem upgrade started, it never completed.
Teltonika support were able to recover it, but we lost all remote access to them.
Be aware that the device will go offline for a long time during the upgrade (the support docs says 15-30 mins) and you'll also brick it if you lose power during the update.
Teltonika said we were the first to have problems... maybe we were. Got lots more to tackle next week...