Personally I do not like at all... I would like them to be banned. For those that say they don't hurt I suggest you put it on yourself.
Below is a link to a report with vet report etc of a dog left in backyard with one on it rained and it malfunctioned and it shocked the dog continuously all day til the family returned to find the dog.
http://www.srdogs.com/Pages/news.apr.may.3.html