I've had some time to play with the Nautilus Radio now...
After hooking it up to my laptop, I was able to see that it had the latest firmware already installed, which is good because I have no access to a real Windows machine. (My only "Windows machine" is Windows 7 running in VirtualBox and that doesn't seem to play well with the Nautilus connected, i.e. errors when connected.) Other than firmware updates, the MacOS version of the desktop program works as expected.
The two button menu system in the 1.02 firmware works great and is intuitive. I was able to conduct the Self Test, Distress Signal Test and SOS Strobe Test. All passed.
For the GPS, it took minutes to lock. (This is much longer than what my Garmin Vivoactive HR takes.) The documentation says it should be faster with subsequent locks. The plan is to get a GPS fix as soon as I get to the dive locale, then once before each dive so that subsequent locks are fast.
There's a feature in the desktop program to show the previous recorded GPS locations. One was in Canada, as expected, since the device is from there. The other looks to be French Polynesia, which is amazing since I bought this used and the last dive location for me was French Polynesia!
There was already an MMSI entered so I'll need Nautilus to issue a reset for me.
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I contacted the liveaboard and they monitor 16 and do boat-to-boat communications on 15 and 17. I set the Chat on the Nautilus to 17 (defaults to 68) and it's easy enough to switch to 15 with the menus.