That is redundancy in my book. I don’t expect holes in my GNSS devices. And if you want to be sure, bring three, because two GNSS units with different readings are not very helpful.

I don't expect holes. But both devices are exposed--something could happen to one of them. And since I like going out in the middle of nowhere I assume I either have to get myself out, or if that's impossible summon help. I don't want a single point of failure on either of these.

Fair enough. A paper map and the ability to navigate offline would be a nice backup, too. Not that I wouldn’t use GPS in distress.