I was sold on armless sunglasses from my first run using them, simply because the secure fit provided by the cord immediately rules out the biggest problem I have with running sunnies, which is that they bounce or slip down your nose when you get sweaty.
The only reason I haven’t been using the Ombraz Refugio more often since I first tested them is that I prefer to use prescription running sunglasses over contacts, so when the chance arose to try the Ombraz Teton with prescription lenses, I jumped at it.