Thats a good idea maxtog. I may try running both horns as well.
How does it sound?
Well, the stock horn, as you know, is puny. But it is faced forward and less obstructive.
Since the Stebel is running via a relay and its own power feed (don't EVER try to run a Stebel power through the horn switch!!!) there is no reason to NOT leave the stock horn also connected. It is there, it works, it is "free", it adds more volume, more coverage, AND redundancy in case the airhorn fails for some reason (mine never has).
Honestly, I can't hear the stock horn at all... because the Stebel is so loud. But I am pretty sure it is working. Now, if I were standing 20 feet in front, perhaps both can be heard, I still expect the Stebel to be much louder, even then. Probably should test that at some point, but it obviously requires two people