It's made of brass or something like that and clamps to the headstock of the guitar. Who knows. I'd try it out before I paid anything for it, or make sure you get a return privilege.
I had a blast last night in a unorganized, overly loud jam at a local bar. I had the only acoustic (versus two hot electrics, a bass guitar and a hundred pounds of gear, and the [ouch] drum kit), plugged into a direct box and into an old PA head. I had a feedback buster in the soundhole and played direct through a Danelectro Chili Dog - a high distortion, relatively low quality octave box that is loads of fun when misused.
I found a neat way to get indefinite sustain. Park yourself about two feet in back and to the side of one of the 3' PA speakers that were sitting on the floor in front of the (ouch) drums. Pretty cool. Feeds back just enough to create pain at the bar for as long as you need to.
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Man, I stayed up way too late and still had to get up at 5...