The good thing with the montana is that the motorcycle mount is only about £45, and the unit can also run Ordnance survey maps (some units come with them) in addition to City Navigator.
If you do not want blue tooth & MP3 player its probably one of the best units on the markwt at the moment, especialy if you ride off road.
There is a great thread running over on ADV rider, some very knowledgeable guys.
I hope this helps.