I tend to laugh at these devices, but then again ...
I sometimes pick a "slow" puncture on my ride, but dont realise until the next morning when it has gone completely flat. If this was a morning of a commute or a club ride, I would be faced with swapping the inner or complete wheel or lifting another bike off the wall and getting it ready, all of which takes time and would make me late and possibly miss the club run.
If the device warned me as I got home, I could repair the puncture at my leaisue overnight.
But still not convinced.