Enthusiasts will like the idea of having a map always on a second screen, the skeptic will say that when you're looking a the map, you're not looking at the game and therefore a "push start for map" solution on a 1 screen handheld is exactly the same... except the "gimmick".
Have you played PSO? A large area map is VERY useful when you need to know where you have already been and where you have not and how to get there