Though all of this thread, I've noticed no comparative data between the Fiamm and Stebel so here ya go!

Db:
Fiamm - 125db
Stebel - 139db

Cost:
Fiamm - $15-18
Stebel - $33-37

Install:
Fiamm - plug and play
Stebel - should use relay

Sound:
Fiamm (high tone) - http://members.cox.net/giaka/horn125db.wav
Stebel (dual tone) - http://www.bikerhiway.com/images/nautilushorn.mp3

"Never underestimate the power of human stupidity" - Robert Heinlein