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My general finding is that the only time I use a bell is when I'm still more than 10 metres from someone who hasn't noticed me and I want to draw their attention to my presence so they can pick a side of the path. If I'm even thinking that I might have to brake then I'm definitely not considering using a bell, partly because the relevant time has passed and partly because it always interferes with bike control (especially on drop-bars)
I'd say that 9 times out of 10 that I see cyclists use a bell, they do it ensure that they don't have to slow down. The classic "it's my right of way!" ringing of a bell, by cyclists who don't want to slow down, is often to try to open a path through a gaggle of pedestrians who've crossed against the lights. It's a douchebag move and doesn't establish priority any more than sounding a horn does.
I'm not sure say anything in an emergency situation is a good idea at all from a cycling perspective. The CA case followed by this cases very much suggest that a cyclists will have it held against them in a way that a motorist using the horn wouldn't.
Much better to keep your mouth shut and if the worst happens rely on the cast iron get out of jail free card of "I didn't see" or "the sun was in my eyes" seams to work fine for motorists.