It’s widely used, but yeah I’m surprised that they’re claiming it’s essential for landings. I though ILS used beacons at the airport, with other beacons for the approach.

Edit: ah, OK, this is why:

“Most airports use alternative approach methods, but some airports, such as Tartu, only use methods that require a GPS signal to support them,” said Jari Paajanen, Finnair’s director of operations.