Its a cool device, that basically allows you to see anything that the computer is monitoring, and it has the ability to record the highest/lowest O2 reading and timing retard during a WOT run (plus the mph that the reading was taken).
A full description is at:
http://www.projecttransam.com/projects6.htm
Biggest benifits (beside O2 reading) is the ability to display current and stored trouble codes in your PCM.
Its a handy little device.