The Zumo 550 has two features I would not want to be without.
1.
TTS. It says to you in .2 miles turn right on 146th Street.
Other units say in .2 miles turn right
2.
Zumo is the only Garmin that does not change custom routes that you create in MapSource and load onto the GPS. All other Garmin units will recalculate that custom route that you spent hours creating.
http://zumoforums.com for great info about it.
And all the other stuff like waterproof, left hand controls, glove friendly touch screen..... the list goes on..
