I got the Pioneer mic and it made a noticeable difference for me. I have a Honda CRV with a factory amp and component speakers (tweeters/mids/sub). My Pioneer now makes much better use of the tweeters and sub using Auto EQ. When I change the listening position to Left Front (Driver), I get perfectly balanced stereo sound.
Some tips:
1. You need to do the calibration somewhere COMPLETELY quiet. Engine off, no talking, no cars passing, no planes overhead, no birds chirping.
2. Put the mic as close to where your ears are when you sit and face the mic forward (usually the front of the driver