I never used a PCII, PCIII to compare, but the PCIII-USB has the Accelerator Pump feature that when enabled, allows you to adjust perameters to give the bike a little more fuel on hard throttle bursts, deleting flat spots. I noticed an immediate difference in my bike in throttle respose and that low-end jerkiness was gone. It has a pretty green light that moves when you rev the bike too...... it makes me feel all warm and fuzzy.............
You won't regret it..... It wakes the bike up, similar to the gearing change from the stock 16/40 gears. It also goves the bike a smoother power delivery, through the entire RPM range, with the proper MAP. Power Commander provides MAPs and a few others can be found at various RC51 sites, or by asking other members what they use.