I love the Nautilus, they are superb. I fit them to all of my cars, but also use a bypass switch so I can disable them when I want to give someone a friendly toot instead of a heart attack.I agree, defensive driving keeps you out of trouble, but sometimes, when you're boxed in and someone encroaches on you, it's the only option.
I drive a little mx5 which had a feeble horn as standard. I replaced it with a Nautilus air horn, commonly fitted to motorbikes, so small enough to squeeze into the mx5. A blast of the Nautilus gets people's attention!