It falls over above 65N especially when there is moderate activity and above.
Also we do polar grid nav during the ATPL's. I believe they use laser INS's these days and portable NDB beacons for the strips. And if your operating commercially there is qualification you need to have I believe which kicks in at 70-75 N/S.
Cirrus doesn't need a ADF it has a Handle in the ceiling in cases of a NDB approach requirement.