The only way to get routes to work on different GPS units is to actually design the route. When I say that, I mean you have to put in alot of waypoints so that from point A to point B, there is only one possible way to get there. It does take alot of time to do, but it works. Then save it in a GPX format, which is a universal format for exchanging gps files. Its not perfect, but its the closest thing to working. Also, www.gpsvisualizer.com has some great tools for exchanging file formats, I've found it very useful. I have the Garmin iphone app on my iphone. Its not perfect and there is no way to upload a gps route to it. Also, when you lose cell signal, you lose routing. I believe this is true regardless of what GPS iphone app you are using. In SW Wisconsin, its easy to lose cell signal.
Let me see. You take the route sheet and put it on your bike and go. Or you spend a lot of time get the route ahead of time and put it into your GPS. I'll take the route sheet it works every time.