Just a thought.
If you're thinking of installing a compass in addition to the C-80 system, you might want to think about a regular old magnetic compass.
It would provide bombproof redundancy (from what I'm told, magnetism is here to stay), and probably a lot cheaper than an electronic compass, and needn't take up much space. There are endless choices. Before you go spend big bucks on a regular navigation compass, consider how often you'll actually be using it (maybe not that often since the electronic systems are very reliable). Something like a smallish "Boy Scout" compass or a kayaker-type compass will work and allow you to locate/relocate it (velcro is wonderful...) anywhere in the boat.
I keep my old "Scout" compass in a small basket beside the helm, and although we haven't had a need to use it - nice to know it's there.
"Be Prepared!"
Casey
C-Dory Naknek