I put one of those on my bike about six months ago. Picked it up from
www.twistedthrottle.com - absolutley brilliant! People get outa my way and start looking around for the train that's bearing down on them now.
However a few weeks ago mine started working on only one note. I contacted the vendor, explained my situation re: shipping costs to australia etc, and they've agreed to replace the horn free under warranty without returning the old one, as long as I pay shipping for the new one. Sounds pretty reasonable to me. I sent them photos of the horn's current mounting, and they strongly advised that I get some tubing and use the included "clean air intake nozzle" for the horn to prevent it happening again.