Mine's electric so I can fit a car horn, as I have to my e-bike. Perhaps it'd have been useful for the driveway incident (I sat there by her car with my arms crossed, waiting for the penny to drop when she saw me halfway off the drive) but, as with the bike, incidents like the T-junction would be too late.

I generally don't find horns useful for their purpose, on any vehicle - usually the first thing you do is avoid the accident first, and the horn then only becomes useful for releasing a signal of disapproval... which isn't helpful or constructive.