The Zumo 550 has...
*XM Radio
*XM Traffic
*MP3 Player
*Bike Mount
*Car Mount
*Audio out
*External microphone
*Bluetooth
*Good phone interface screen should you decide to pair Bluetooth phone
*Waterproof
*Create routes & waypoints offline & upload to Zumo
*Download routes traveled to PC, extract lots of interesting info (exact locations, speed, altitude, etc. etc. etc). Export to other users' Zumos
*Import custom points of interest
*Interface customized to fat-fingered/gloved biker hands
*Combination of hard (rubber covered, on left of unit) and soft buttons (on screen) make selection of options easy without taking attention off of the road
This is not a perfect unit (Bluetooth is mono only, and screen is a bit too small), but it is pretty darn close. You can get other GPS units to do some of the same things, but I doubt that you will find another that has so many useful features in one unit. My guess is that if you never had a Zumo, you may be perfectly happy. However, once you have one, you will never want to be without it. It is truly a must-have that no other GPS will replace - not even the new Zumo 660!
You truly do get what you pay for.
Ed