Note that the Montana does not have bluetooth, but the Zumo 660, 665, & 350LM do.
The Zumo 660 and 665 can display tracks; the 350LM cannot (except to backtrack on its own track). In my view, this makes the Zumo 350LM the most street-oriented and least versatile of them all.
So, if you need bluetooth AND visible tracks, it is Zumo 660 or 665. If you do not need bluetooth, I think the Montana offers more versatility than a Zumo.
Just my humble $0.02 - I am no expert.
Eventual Master of the Obvious
2005 R1200GS | 2013 R1200GSW | SOHC4 208 | DoD 2032 | BMWMOA | BMWRA | YB