I have a sporn harness and it used to work really well, however she is at times starting to pull right through it. It works because the straps that go round the legs tighten as she pulls...
Although they are really good, I would rather I had trained her to walk nicely on the lead. I would advise anyone with a puppy to do this first! I am going to try in the summer to go back to collar and lead when I'm not at work and have time to walk and not worry if we don't move anywhere!