Fits well, sleek and light, moves with my dog but still secure. I like that the pockets are stretchy so the vest doesn't flop around even with stuff in them, and it's nice to have 3 separate pockets. The included water bladders are the perfect size. The loop to attach the leash to seems secure. I can easily fit his light-up harness over this which is nice too. I appreciate that it seems like his shoulders still have good range of motion in the vest and even if he pulls a little, it doesn't seem to restrict him in any way and the front straps are broad and soft enough that it seems comfortable. We've had it for several months now. For reference, he's 55 pounds, deep-chested but lean (German shorthaired pointer mix), and the medium is perfect, we used the sizing chart. I love this vest for running!