I bought a WYDWL harness but my pup learned how to pull on it, so it does not help at all, in my experience. In fact, on our first outing with it, he pulled me over and I sustained a serious injury when I face planted in the middle of a road!
I realise lots of people are happy with theirs.
I emailed the company last night, to ask for advice. I'll post again if they come up with anything useful.