Just updated my Montana 600 via webupdater, 3 minutes than it was finished.
When I rebooted my Montana, it first said "validating update", loaded it from 0 to 100% then "loading software"
Once started, everything looked fine, but no GPS!

After 10 minutes, it found the GPS, such as it was a cold start, and after a re-calibration of the compass, everything was fine.

My unlocked maps are still usable.

So, don't hesitate and go for it! ;-)

Rithon