I wasn't sure how this no-pull harness would work. I was also questioning how it could fit S.M %26 L dogs, but it fit my 20lb. dog perfectly. I have noticed he has not tried to yank my arm out of its socket since using the new harness, but it's not completely failsafe. It definitely has made a difference in less tugging. I was pleasantly surprised by the harness; however, the plastic fastener will surely be the first thing to fail. His other harness has a metal fastener which is much easier to use. Overall, not a bad option