I'm the guy that installed the Bad Boy horn in my 2018 Leaf. Unfortunately, the Bad Boy has gone bad- now blowing fuses and seems to be shorted out. The short may have to do with the fact that the unit had to be mounted upside down in order to attach it to the car the way I did. I have a feeling water got into it.
So just replaced it with a simple low-tone horn from Amazon. Seems to work great, doesn't blow the normal 10A fuse, and this horn actually beeps when you lock the car (the Bad Boy didn't). Success!!