I've got one, mounted in a similar position to the Shimano display (behind the bars, to the right of the stem, using the bracket that came with it) - much more crash proof than mounting it above the bars, and reasonably discreet. I like knowing how far I've ridden and when the speed limiter is about to kick in, and also it has more accurate battery charge percentage indicator than the blue lights on the top tube.
I suppose you could do the same with a Garmin, but I don't think the battery lasts very long compared to the Specialized display (which is more like a "normal" bike speedometer - fit & forget) - and I certainly wouldn't have a smartphone clamped on anywhere, as that would be the opposite of crash proof.
It's not perfect - there's a bit of a knack to resetting the odometer, but I'm happy with it.