I recently installed one and am still working on interpreting the data that it gives me. The instructions are only for the functions, you still have to work with the tach to figure out how to record multiple runs and get the software to do what you want it to do. I've never used the playback function to display a run on the tach as I bought a cheap ole laptop to take to the track.. If you enter the data from the timeslip into the run, it can tell you a bunch from one run to the next. It only takes a minute or so to download a run and be able to review it. The hardest thing about using it is that you must remember to push a couple of buttons just before the run.
A couple of negative observations: The shift light included is small and I don't believe is very effective during daylight hours. I don't know if they have another one that would plug into the tach, but have considered giving Autometer a call. To get the driveshaft speed, magnets must be J-B welded to the U-joints, although a collar is available at extra cost from Autometer that should work better.
Irregardless, it is a pretty cool data logger alternative if you don't need or want all the other motor inputs.
Here is a copy of one of my old runs as it is seen on the computer:
Shows a car bogging going into second gear (stick shift car.) Note that the launch RPM (off a 2 step), shift rpm's and activity times are recorded.