Mostly I'm pondering if this would be useful for them in the (very unlikely) case that they get into a situation where they can't dial 911 (need to be quiet or

Mostly I'm pondering if this would be useful for them in the (very unlikely) case that they get into a situation where they can't dial 911 (need to be quiet or otherwise don't want to draw attention to themselves). But, as others point out, actually remembering the app exists when you need it may be problemmatic. And even so they would then have to find it on screen 27, past all the 2048, angry bird, and flappy bird games and things.