Knowing how to use the OBS facility on a GPS is a critical requirement too.
As indeed is having an OBS facility. As an IMCR holder who flies less often than he would like to, but almost always includes an IAP on every flight to remain current (even if it's only an ILS into home base) I use the OBS hold mode a lot to 'monitor' NDB approaches. Skydemon don't offer an OBS hold mode and that feature alone pushed me back to Garmin for my new GPS last year.
Tim