Did you ever find a solution to the lack of manual network selection. We have started using the MG21Es with mutli/world SIMs and also find the auto network selection to not be optimal. Sometimes results in the unit connecting via 3G when a perfectly good 4G signal is available on another network. Our sites often run on temporary generator power which is shut down overnight so it might work one day and then the next day we end up with a different carrier.
Manual network selection options are needed, have this on a 'basic' brand 4G modem/router which is also a quarter of the price. Also any manual APN settings have to be done locally on the device and cannot be set via the Meraki dashboard. Nice idea having the management all in one place but not sure these units are quite up to scratch yet.
Just seen a MG41E is about to launch, perhaps this may improve on this.