As I understand it, the PF-7 module adds additional tuning so that the null can be adjusted in the RF range more effectively. Ron (of course) could explain it best. For instruments that are not as quiet as you would like, and adjusting the null controls doesn't help (much), I would say the difference is night and day. It certainly was in the case of my bass. The air is getting increasingly stuffed with RF these days, and while some basses may be fine without the PF-7, some absolutely require it... at least for critical applications, like studio-work.