“What is the difference between the GTM 60 digital 3d traffic receiver and the receiver that comes with the Garmin 2457 LMT? I am still confused about the difference between the GTM 60 digital 3d traffic receiver and the receiver that comes with the Garmin 2457 LMT? Is there an advantage of getting the GTM 60 digital 3d traffic receiver rather than using the one that comes with the Garmin 2457LMT? Thanks.”