Auto shutoff toilet valves - has anyone used one?

[Matt Fitzgerald]

One of my biggest peeves is a steep water bill.  I hate when toilets run or in one case overflowed and tenants don't tell me about it.  Has anyone ever used an auto shut off valve when a leak is detected? Specifically I'm looking at this one

http://aquaone.com/category/toilet-guardian-products/ Any pros or cons that you've experienced?  Thanks.