I have a Garmin Vista HcX. I've used it on two tours. I downloaded the gps information from two Adventure Cycling tours - the Lewis and Clark and the Great Divide. For the Lewis and Clark I bought the DVD with street maps. For the Great Divide I bought the DVD with topo maps.

On the first tour the gps was barely helpful - mostly because I didn't know how to set it up and use the ACD waypoints. You have to create your own routes and import the waypoints you want - ACA gives you every possible waypoint on multiple (alternative) routes. The gps doesn't have any idea where you want to go.

By the time I was preparing for the Great Divide, I had done some more research and had a better idea. It took many hours to import waypoints and create routes for the first 14 days of my tour. I ran out of time. If I had ridden more than 14 days I would have had to rely on maps. That wouldn't have been a bad thing, I guess, because I made at least one mistake in setting things up, and one day my gps was telling me to go straight when everyone with a map was telling me to turn right. We sat and discussed it for awhile, then decided to follow the map. Good thing! Also there are places where the Garmin topo maps don't show the trails or roads that the Great Divide follows. It won't let you "bushwack" - instead it tries to backtrack and go around to get to the next waypoint.

My conclusion for my experience with the Great Divide route was that the gps was very helpful (and really convenient - no stopping to peer at maps, no unfolding and refolding, stuffing and restuffing maps into map pockets) - especially to confirm what those with the maps had said, but the bottom line was that the maps were better.

On my road tour the gps came in handy a few times for things like finding motels and finding restaurants. I also dropped off a rental car somewhere in Portland, Oregon (Alamo's terminal isn't close to the airport - who'd a thunk?) and had to ride to the Amtrak station, which was several miles away. The gps took me right there. It put me on a busy arterial with no shoulder, but it was easy to move a block away and stay on track. (The little gps doesn't say "Recalculating", it just beeps.

The topo maps didn't have any points of interest, so I couldn't use it for finding motels, restaurants, etc. on the Great Divide tour. Luckily one of my mates had an Iphone. He took care of all of that kind of thing.