The antenna FB is describing provides cellphone coverage. Wireless providers just provide Internet/network capacity (since they rely on a customer's fixed antenna). Both those things are needed in rural areas.
Both these solutions require that you be in line-of-sight to the tower. You are more likely to be in line-of-sight to 250 meter tower.
There are many competitors that use an omnidirectional tower and directional antennas at customer sites.
A recent competitor in this space regularly achieves 6 miles at >100Mbps (~16mbps uplink):
https://www.telecompetitor.com/wisps-get-cbrs-range-as-great...
FB is claiming 6Mbps down (1.2 up) at 12 miles for their approach, which doesn’t seem to rely on fixed location customer antennas.