They have 2 different products:
Mobile Broadband and
Home Broadband.
Mobile broadband is available everywhere, like a normal mobile data plan. I guess the level of service that is acceptable for them is lower here?
Home broadband only seems to be available in areas with very good coverage and capacity, e.g.: where they deploy the "Phase 8" masts (see
this video). These sites provide 4G + 5G, fast speeds (+1Gbps), and better indoors coverage (B20 and B28). Their product page mentions "150Mbps" average download speeds for this product. I've seen +800Mbps in London with my phone.
Their deployment of these masts is being delayed or stopped in some areas. Too many
nimbys out there complaining about the looks of the mast, that "5G spreads covid" (lol), etc, and councils reject their applications...
I doubt they'll install these in places without a large density of people, so I don't know how this "home broadband" would work in rural areas. They are upgrading existing sites, but I don't think they have the capacity to provide +100Mbps reliably to many customers in places where each tower covers large areas and rely on long range, but slower bands like B20 and B28.
Anyway, I've read that there's a trick to order "home broadband" even where it's not available (use the post code of a place where it's available, then add your address when ordering?). I doubt they'll care if performance isn't what you expect though, so do this at your own risk.