To answer my own question - it's embarrassing, but the computer was not seated correctly in the cradle. Unfortunately, in the wrong orientation, it still lit up and showed up as /dev/tty.SLAB_USBtoUART when plugged in. Furthermore, the m2 manual shows it in the cradle incorrectly (cable at 10:00, buckle at 3:00 - should be cable at 10:00, buckle at 9:00).
As for getting rid of the device buttons, they can be deleted by modifying //Users/<username>/Library/Preferencesorg.hohndel.subsurface.Subsurface.plist.