Dunno why I didn't think of this. Japan, you've done it again.
In my life I have most needed one of these bells in the streets and subway platforms of Hong Kong, and in KLCC mall in Kuala Lumpur. Although having said that, in neither of those places are the people so unfailingly polite as the Japanese, so I'm not sure how effective it would be.
The other problem is that the average dawdling teenager probably has an iPod playing while they dawdle, which possibly neutralizes the bell.