China warranty only, but usually huawei modems rarely break down, unless power surge by lightning which pretty voids the warranty anywhere
I'm using it my for my cctv using hikvision cameras, since I don't use the ezviz cloud I just use portforwarding on the router with vpn.
Technically with ipv6, you can connect to your cameras without portfowarding, still figuring out how to properly setup ipv6.
So once setup digi apn profile, can make calls/receive on VoLTe without it dropping to 3g? Even if the person calling don't have VoLTE enabled?

Still using ipv4 + vpn, don't know know properly setup ipv6
Might need a new router for that
You're not using ezviz cloud?