Garmin etrex Vista and Linux

I have a new (to me) ancient Garmin etrex Vista handheld GPS ($30, ebay). It has a custom serial connector on the back, takes AA batteries, and happily talks in MGRS in addition to degree-minute-second. MGRS was the key - I need it to be compatible when I go out to the field with the Army Reserve.

Onboard features:
Discovering the Software Version and Unit ID: Main Menu -> Setup -> System -> (Zoom) Software Version.

Problem #1:
The date is showing as 2051. That's a known bug, and this page shows how to fix it by hard-resetting the device.

Gpsbabel:
The gpsbabel package, in the Debian Archives and Ubuntu Repositories, can transfer waypoints, tracks, and routes (but not maps) to/from the device. See the online documentation. It's a command-line application. Here are some example commands:

gpsbabel -D9                                                           # Debug verbose flag
gpsbabel -i garmin,get_posn -f /dev/ttyUSB0 -o kml -F myposition.kml   # Get current position
gpsbabel -o garmin,power_off -F /dev/ttyS0                             # Send power-off command