HKS Turbo Timer (Type 0) It allows you to set a predetermined time that the car will run-on for after the key is removed from the ignition. This allows the turbo to cool down and the fans to run to dissipate the heat. Also, the oil fed through the turbo will cool off and prevent the oil from coking and seizing the turbo. HKS Turbo Timer (Type 1) In addition to the functions of the type 0 TT, type 1 adds two memories (for timer "on" time) and a 4-digit LCD display that can measure vehicle speed/peak speed, a speed warning, RPM (w/peak hold), RPM warning (for shift-light or red zone applications), interval/lap timer, as well as 60', 1/8 mile, 1/4 mile and 0-60 MPH time.
Essentially the type 1 has more functions and costs more, I wanted one for the functions but couldn't justify spending £90+ more than I did on my apexi style one.