We used to have a DAR here in Utah, a retired FAA employee, who also insisted on a magnetic compass on machines he inspected. Our PRA chapter almost bought one which could be loaned out and attached with velcro, just for the inspections.
I can see both sides of this debate. I think about the guys who trailer minimalist machines out to dry lakes here in the west to fly on weekends. They often stay within visual line-of-sight of the trailers that brought them. They're too heavy and fast to be ultralights, but their mission profile is the same. They have N-numbers, but a compass is not required for this kind of flying.
If you're relying on multiple redundant electronic devices for navigation, a dedicated, calibrated compass seems like a pretty easy decision. I've been listening recently to podcasts from commercial drone pilots, and they all say they've been surprised by dead batteries when using phones and tablets in cold weather, as one example of a failure mode.
