The Montana works good on my GS too. I love the mount and like Emmbeedee found ways to move it around, though I do have 2 mounts now also.
The rugged mount is very solid, when locked the GPS is pretty darn secure, if you're parking in an area where you're so worried that you think the TT will help, you should just take the GPS off the bike IMO. Either mount could be ripped off the bike by a determined thief. I just put my helmet on top to cover the GPS in my travels, always parking the bike right in front.
The home made bracket on top of an Otterbox works great and put the GPS in a perfect spot.
It's like the modern equivalent of a GPSMAP 276/478 with all the options (unlike the Zumo) , except with no limits on tracks points or number of tracks that can be loaded and displayed at one time, has a big touchscreen, etc.
I use City Nav map, but the Montana also has the ability to load Satellite Imagery that displays with City Nav, letting me see what's actually around me, and not just what's in the "map".
The Montana's ability to work with tracks is also far superior to other units, as mentioned already.
Couple of screen shots from the unit to demonstrate the satellite imagery, it's very useful feature for ADV riding.
On my recent CDT, TAT ride I had about 10 miles of high-def SI on either side of the tracks the whole way.... priceless to scout for campsites, optional trails, etc....
Here's how you get the satellite imagery, or TOPO maps in Bascamp, selecting the ares you want:
It's been a most useful tool for me while on long distance off road travel adventures, great for local area exploring also.
Here's the Garmin Montana thread in Layin' Down the Tracks for more info: