I love these tights! I followed the size guide and purchased XS/4 and they fit perfectly (I am 5'4" and weigh 125 lbs). I have done several runs in them. They are quite lightweight, so they are great for "shoulder seasons".
Love my "Sea of Dreams" Run-wild tights :) Have so far used them for running, hiking, and even just wearing around the house. I also have the "Forest Friends" Athletic tights which I love, but I'm finding the fit of the Run-wild is just a touch better for my body type, especially in the waist, hips, glutes. The waistband fits a little tighter, is shaped rather than a straight across seam and I love the 2 pockets, one on either side of the waistband. And yup, they stay do stay up! Would definitely get another pair and am also looking forward to trying the shorts in this style :)