I see you're in England. According to Wikipedia, "In the UK, over 3,000 have been sold, mainly for use outside shops and near transport hubs." Although there may not be any exactly where you live. But it seems that the public sense of controversy surrounding these devices is greatest in the UK.
Personally, I've done some amateur testing on myself and I believe I can hear as high as 18,500 hz, if the volume is loud enough. I remember when I was a teenager I could hear up to 19,000. I can't explain why my upper threshold has diminished so little by age 32, compared to other people. A tinnitus specialist I saw believes that my brain is simply hypersensitive and hyper-aware of all stimuli. He told me my brain is "missing a filter" that other people have, and that's the reason I have tinnitus, in his opinion.