I agree with Rooky and Scratch about the supplier; Action Electronics at Component Shop, but not necessarily with the the choice of horn!
You want a deep tone foghorn so go for the P13 Foghorn module which is designed to do that.
The Twin Tone is more of a car / boat "coming through , get outta my way" type of horn.
Link and specs attached.
You will need at least a 4" speaker for the best sound though.
You might also consider an RC switch to activate the horn - such as the P43 single, or the P44 double switch would allow you to operate some lights as well.
The P43 is out of stock at Component Shop but you might find a dealer on Ebay or Google who has one.
The switches are easy to wire up and work very well👍
Cheers, Doug 😎