The DRBIII has some very valuable functions if you're working on your own car, or plan on engine mods. It will read/ID/reset codes. It will also allow you limited access to the ECU/FMS computers to read engine parameters/diagnose problems and reflash software and do some programming mods.

The downside is the damned thing cost nearly $8,000, or you can rent one from the manufacturer for a mere $1,500 per week.