I've got one of these,Sure they are - you need the right kind of a bell that allows for a loud ring and a soft ring, and its the cyclists job to learn how to use the thing. Give me a polite ring every time over some clown talking over my shoulder.
It's decent, I use it all the time. I'm on my second one because I reefed the arm thing off it because I was constantly putting the bike on my shoulder and it caught on my jacket or something.
It just makes the one sound, you can kind of modulate the volume a bit, but it's a nice bright ping.
And then I usually follow that up with a friendly "get out of my fucking way you absolute CUNT", as I'm vigorously flipping them off as I brush uncomfortably close past them.