The first thing everyone needs to learn is that there are people who swear by pretty much any product ever sold, including Yugo's. My point being, just because some people swore BY Power Commanders (as opposed to swearing AT them), that doesn't mean you should blindly follow.
First, are you talking about the old fashioned Power Commander piggyback device, current version called a PC-V, or are you talking about a Power Vision which is also a product from DynoJet. There is a huge difference, with the Power Vision being a modern flash tuning system versus that old add-on box from Power Commander. Anyone running a modern Harley (2007 and later with closed loop engine management) would be better served with a flash tuning system. Those include the SEPST from Harley, the Power Vision, the TTS Master Tune, and others. If you plan to have the bike professionally dyno tuned, I'd suggest spending your time finding a top notch tuning person first, and then discuss the choice of system with him.
JMHO - Jerry