GPS systems which are reliable but unapproved
Reliability of GPS is often overestimated. With the solar activity on the rise, many specialists predict more frequent loss of GPS reception in the coming years, and loss of reception due to aurora borealis is a fact. I am not trying to assert that ADF is any better, but relying on GPS alone does not look like good airmanship to me. Personally, I wouln't want to fly over the North Atlantic without a non-GPS backup to GPS - e.g. Loran (for lack of an affordable INS).