A bit late to the party.....

You may want to try a 3 mobile SIM. As they piggy back EE towers signal should be good. A guy from the Spiceworks forum posted that he used APN: 3internet for a variety of 4G routers and was able to dial into each one using its public IP and DYNDNS. He even sent me a link so i could see it working!.

Hope this works for you.

I don't care which towers they use, but in my experience the Three signal very much depends on where you are. I'm in Cardiff, a capital city - 5G more or less non-existent. If I visit Caerphilly, just up the road and expanded so much it's nearly a suburb, I have no mobile signal at all.

Piste Basher wrote: ...in my experience the Three signal very much depends on where you are. I'm in Cardiff...

Same across the water, in North Devon. While idling away the time in Dunelm's car park in Barnstaple, I did a speed test using Three that came back as 80/20 (which is significantly faster than my home broadband). However, back at said home, the Three speed test just times out

On the plus side, I didn't actually pay for the Three SIM which comes with 250Mb of free data per month! (I can't remember how I acquired it...)