I have the factory nav, a pda nav, and my wife carries a Garmin nav.
Many old map-readers see no advantage to a nav and that's fine with me.
Some aftermarket users have nothing good to say about the factory nav and that’s fine with me also. Personally, of the three, I like the nav on the bike the best.
My wife and I are leaving on a 15-day 4500-mile trip this Friday and I am taking no maps, no itinerary except we want to be in Key West halfway through the trip. I am stopping at the state’s welcome centers for discount coupons and finding motels when we get tired. We’ll eat when we get hungry. This would be really tough to do without a nav and the database in it.
I think a nav is worth it.