Depends on what razr you had. I think they changed the port to a micro usb in one version.You should look again. I use 2 old Razr chargers (1 home & 1 car) and they both fit perfectly.
If the charger is marked 1 A, it'll charge faster
Good point. Some devices(not the hero) will complain that the charger is not compatible but 95% of them will still charge. They just throw up that warning b/c they will charge slower.
If you are constantly using GPS then you will want to hunt around for a 1 amp version because even with a 1A charger the hero's battery can't keep up with the drain of GPS and data for the navigation.