I happened several weeks ago to have some people in at a meeting who were talking about these things (and worse!), and was (a) gobsmacked such things existed and were commonly being carried especially by young people, and (b) by the fact that they were actually not illegal!
On a separate note, we afterwards had a long conversation with our building security who let two people carrying a huge array of offensive weapons enter a public building without being stopped or questioned during ahightened security alert period!!!!
For those who think it's probably illegal, after what I saw paraded as "defensive" in that meeting, I would lay bets that you are actually wrong. I was appalled.