I have recently bought Huawei USB modem and discovered that these things run Linux with Android. This is pretty off-putting. With such a modem it is no longer enough to keep your system & drivers up to date, because the device has it's own full-blown operating system. An attacker no longer needs to hack your machine to capture your traffic or make you a part of a botnet, it can hack your modem. And the modem, like Android phones, is probably not going to receive software updates for long.
There is a large selection of routers or general purpose devices that can be used as routers (for example Rasberry Pi) on which you can easily run standard Linux distributions. You can configure such distribution to install software updates automatically and have a quite secure setup for years.
With these USB modems, although they run Linux & Android, the images are of course proprietary and you fully rely on Huawei for security patches. The patches also don't install automatically, you need to check for them, download and install by yourself.
Most IoT devices have the same problem, so I personally avoid buying them, although they can work behind your home firewall, which can protect against many remote attacks. GSM modem is your gateway to the internet, so you can't put a firewall at front of it.
