Sentinel MDT-1 Vs. HID-2

Hi I am trying to figure out what the differences between these two unit are. The MDT-1 and HID-2MDT-1 $191.99 http://grow-gps.com/products/digital-timers/and HID-2 $164.99 http://grow-gps.com/products/lighting-control-power-expansion/The only difference I see is they are in different housings and the MDT-1 has 4 outlets and the HID-2 . What am I missing?