I installed a Voyager on my KTM 450 EXC and I currently have a Garmin Montana that I use on all my bikes.
The Voyager is a nice all in one unit but has limitations as a GPS. When I was using it on my 450 I was mainly using it to lay some 'bread crumbs' out as I was exploring. On a couple of rides I actually load up some GPX files to follow. The issue with the Voyager is when you come to a spot that you thought went through that didn't or when you need to find the nearest gas station. You really cannot navigate on the fly with the unit unless you have preloaded everything.
The Montana is nice because it gives you the flexibility to navigate on the fly if you run into trouble or just want to find another route. Use that with Basecamp (We are learning to play nice together - not exactly the most user friendly software that is out there) and it works out pretty well.
My buddy usually runs two or three GPS's at once on his bike. I always thought that did not make any sense but after navigating a couple of DS rides I understand why he does it. It is nice to keep one GPS zoomed in tight in the area that you are riding and at least one other zoomed out for the big picture. That allows you to make some pretty quick decisions when it comes to changing a route up. You can do the same thing on one GPS but you have to constantly zoom out and back in to get an idea of what is going on.
I just picked up a 2011 TE250 one owner bike with 281 miles on it. I am planning to use this bike for woods riding up in the GA, NC, and TN mountains in a base camp type scenario. This means I generally won't be carrying much on the bike and I would like to keep things to a minimum. In this case I think the Voyager would be the ideal unit to have since most of the riding will be exploring the various FS roads and trails. Generally most rides tend to be under 60 or 70 miles and start and stop from camp.