If it doesn’t produce vapor at all, there’s no way for anyone to actually know you’re vaping if you’re using one of the small ones and in no way does it affect anyone but you. Would I walk around the park using it? No, but a well timed bathroom break would work. They aren’t going to have cameras in the stalls...at least not yet.
They really are undetectable. My kids are teachers and they’ve learned the signals that they’re being used. Kids will vape right in class and they can’t tell by smell or sight.