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They work very reliably. I live in Manhattan where density of addresses is obviously quite high, so when I have a notification, for example, for home, it may go off within a block or two as I'm walking home, but it's consistent and one of my most used features.
 
I've had horrible luck with them. I'd set them while on wifi and they'd get triggered when I passed by a certain cell tower three miles away. It kept happening to me so much I finally gave up on them.
 
I think having location turn your ringer on/off based on location would be nice, don't think that is possible though.
 
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