The PCIIIr (which I have) has the capability of tweaking the ignition timing.
That was the main difference between prior units (PCII and PCIII).
While nice for race teams, it's overkill for the casual rider or one who doesn't have the resources to monitor the engine during testing.
The engines are at a high state of tune already, and it doesn't take much to cause a overheating, pre-ignition, or detonation state if advanced too much.
Be very careful if you decide to play with the timing.
The PCIIIUSB is modular in design and has various add-on modules for more functions.
Like ignition timing, quick-shifter, etc. They even have a hub for everything to plug into.
Another slight advantage it has over the older units is that it samples the engine every 250 RPM vs. 500 RPM of the older units. On paper it allows more fueling accuracy.