Want to learn everything there is to know about the Montana? Go: http://garminmontanagpsr.wikispaces.com/Features
Then, since the device is nearly useless without the Garmin software and maps: http://garminbasecamp.wikispaces.com/
Be prepared for a steep learning curve. See: http://advrider.com/forums/showthread.php?t=688775 (and the next 500 pages)
One of the most important things in a motorcycle GPS is screen readability, all the older units fail miserably in this regard, and you have to stop to read the GPS accurately. The Garmin Montana wins the readability competition in all conditions hands down.
Beware! It's a very deep rabbit hole! The purchase cost (~$400) is only the beginning.