I think there are ways of using the harness.

For DD1, she was very compliant and really it was for my mum's peace of mind when taking her out by herself. DD2 is a bolter and it really saved her on many occasions.

my rule is to hold hand whilst wearing it, i.e. not just holding the end like a dog lead and looping the loop through my wrist for my own peace of mind unless both hands are busy (when opening my purse for example).