The multicheck that Tony want's to install can be used for tuning purposes. It will read out injector duty cycle, MAF voltage, rpm among other things.
The rev/speed meter I have it purely a toy that looks cool.
Meter's revs speed some timing functions, 0-100/200/400m, 0-100/200/300km, peak hold functions and a trip odometer. Speed and rev trigger outputs. There may be others but I forgot them.