Also if anyone catches you with a shoe cam they will not be thinking you’re shooting feet and instead think you are trying to upskirt. Upskirting is pretty much illegal in every country and can end up with the police being called. Even if they find nothing illegal it’s a hassle that’s not worth it.
Addressing this as I thought my stating you should ask first for permission would have explained how I wanted to avoid this, but I guess not. this is my concern with most candid shots. State and country dependent you can be free to do what you want all the way to jail time, all it takes is someone spotting it and making a fuss. Asking permission is always a better route, if occasionally awkward.
I brought up the shoe cam as thats how people used to do it before phone cams caught up to proper photographers camera quality.