My mom got one for my 4 year old at POR in October. I think she said she had to give them her CC # so they would charge her if she didn't bring it back at the end of the week. We just kept a really good eye on it.
We got one b/c she had never been around a hot tub before and went down the steps into the center, and it was over her head. We struggled to get to her b/c there were people all around the edges of the hot tub. Luckily, we got her before anything happened. She avoided the hot tub after that.