Unlike the Mu-Tron, however, the Ibanez AF9 uses a battery or a standard 9v adapter instead of a proprietary power supply (useful if you're using a pedal board or daisy-chain adapter). The controls are the same (Level, Peak, Filter, Drive and Range) as the Mu-Tron, but with a slightly different configuration.
The biggest advantage the AF9 has over the Mu-Tron is the price: where a Mu-Tron will cost you $700-$800, an original AF9 goes for around $100-$150 (which is less than the Maxon reissue as well).
If you're a collector, though, consider the Musitronics; since the AF9 was reissued, prices for the original version have decreased.
What does it do? The AF9 is an automatic envelope filter. This means that, like a wah-wah pedal, the circuit varies the shape of the "Q" or equalization curve of the signal. This causes a wah-like effect, but unlike a wah, you don't control the sweep yourself. The settings on the pedal determine the depth, peak, and direction of the control sweep, and the level to which the pedal is sensitive to pick attack.
The sensitivity control allows you to play with the pedal on, and minimize its effect by reducing the volume of the guitar, or picking more softly, then exaggerating it by increasing pick attack and volume. The direction setting allows you to have your signal "wah" up or "wow" down with each note. The drive level gives a little boost to your signal as it passes through the filter circuit (this works especially well when paired with another distortion/overdrive, much like the depth setting on the WH10 wah-wah pedal).
Aside from its obvious uses as a source of "quack" for funk, reggae, jazz, or anytime you just need a funky, skanky backing rhythm, the pedal performs well as a mid- and treble booster as well. If you use a TS9 or similar overdrive, and run it into the AF9 at a high gain level, you get a great, fully open sound not unlike leaving your wah in the "sweet spot". After fiddling with the dials a bit, I found I was able to keep my guitar in that "sweet spot" no matter where on the neck I was playing. This doesn't work well for chords, but it has great potential for lead playing.
Highs:-Great at what it does
Lows:-Doesn't do much else
-A bit noisy (esp. with too many other pedals)