I find them disgusting and demeaning. I'd never use one, not ever. We don't have them thingies here and when I first came over to the UK and saw kids on a dog leash, I was shocked.
I used to take my kid places where it wasn't dangerous and where he could run free, like nice parks, our garden, etc.
For streets, etc, he had to sit in a buggy and when he was older, it was either hold my hand or sit in buggy.