From DarrylW4
Positive:
1) Excellent display, great color, detail and easy to read
2) Superior reception in difficult locations. The 400t has been able to acquire in the apartment, a feat the GPSMap 60CSx has also done, but the Colorado is faster with better signal strength.
3) Great next generation interface. The new interface is intuitive, easy to navigate, and well executed.

Negative:
1) Works only as a mass storage device. Unlike previous Garmin outdoor units, this one goes into Mass Storage mode when connected to a computer locking out the GPSRs functionality and limiting access from the computer to disk mode. This means that applications relying on GPSBabel such as GSAK and MacCaching are not able to talk with the unit.
2) Geocaches can not be edited There's no functionality within the unit to mark a cache as having been found, nor options to change coordinates for those puzzle caches, or even to add a new geocache from the unit. Geocaches are all loaded through the disk mode into the GPX directory on the unit.
3) Geocaches and Waypoints are not displayed on the map. Waypoints are displayed in certain modes when zooming in, but Geocaches are never displayed on the map. Even when routing to a geocache the unit will display a blue pin icon rather than a geocache icon.