Solwise Net 434t 'proper 3G router' is being used for LEL at a couple of controls, , £100 - seems expensive but performance is exceptional, both the wireless and 3G - we have used it in areas of poor coverage where mobile devices just don't cut it. - If need be you can add an external antenna. Any mi-fi device with internal patch antenna won't match it. You can also connect a PSTN telephone, - mobile phone & data together.
Lots of config in the box - Qos, filtering, routing, AP LAN/WAN and... more. There is a cheaper Solwise device without the PSTN and only two ethernet ports.
- writing this while you added your reply. - Not relevant to you V.