The real advantage of an open source gateway based would be that you can throw away the vendor silliness and just make your own remote-administration-optimized build using the plain Semtech packet forwarder and daemons to manage whatever Internet backhaul solution you pick.
Typically you wouldn’t be doing much runtime configuration, because you’d have most of your needs baked into your deployment image.
Though if you don’t chose to throw it away, LUCI based configuration stuff tends to be scripting that’s in source form on the box anyway.