I have not owned a Garmin so I cannot comment on them. However, I have had no problems with the Magellan locking onto satellites under tree cover with one exception. While in a pine tree grove up in the Poconos last November I repeatedly lost the signal each time I entered that particular grove. That was the only time it happened but I thought it was worthy of mentioning.

As someone mentioned above I believe antenna placement and type is the key to this issue.