Before a unit like this will work it has to have a strong mobile (cellular) signal, preferably at least 3G, better 4G.
I don't know about other networks, but I have a phone on EE and another on O2. Both have huge data blackspots in the countryside, and my EE one fails more than it succeeds.
Particularly if you are heading into the boondocks you would be well advised to check the 3G and 4G coverage maps of the company associated with the SIM on the device.
Otherwise you may be drawn to the conclusion that coverage where you are is rubbish, and the device was of no use at all.
You don't say where "rural England" is, but I live in some.
Most of Devon and a lot of Wales is a dead loss, too.