Price
The Tracker 4 is effectively the Tracker 3, which a few amendments, including a rubberized over-molded case, larger LED display and the same Tracker interface. Signal suppression and Big Picture modes for no-nonsense multiple-victim searching. Motion-sensing auto revert-to-transmit mode. Upgradeable software and electronics performance testing for fleet management.
So what's the difference between the Tracker 3 and Tracker 4? Essentially the case - the Tracker 4 has a strong, rubberized case making it a more durable transceiver. It also has a larger, brighter screen and louder speaker.