I have had a Montana 600 for six years, used primarily for geocaching. The device has developed some physical issues so I splurged and replaced it with a Montana 680. The differences are taking some time to figure out.
Right now, on the MAP view, the 600 displays the icon for the found caches while the 680 does not. I have the same GPX files in both, so I know the found caches are there. Is there some setting I have not found yet on the 680 to make it display like the 600 does?