I have the 500 and I find that it meets my needs... I also use it for navigation as well. When I do a organized supported ride, I contact the organizer ahead of time for a cue sheet, then use ride with GPS to make a .tcx file that I load on the garmin. This will keep me on the route. It won't tell me street names, but it does tell me when to turn, and I can see where I am and where the course is. So if I do get lost, I can see which way I need to head to get back on course.
The 500 does have issues sometimes with longer 100+ mile courses with alot of turns. It can tend to hangup occasionally while doing those routes.