We used to put our dog in a spare hiking pack and had put off buying a purpose-made dog backpack for a while because we weren't sure it would be worth the cost. We were so wrong!! The difference is huge. My 15kg staffy feels so much lighter. She looks more comfortable and doesn't move around as much because of the built in harness. I can carry her up mountains for hours on end whereas before I was taking a break every 20 minutes to readjust the pack. 100% worth it would buy again. It lets us take our senior girl to places she never would have gone on her own and smell all the best sniffs on top of the mountain! Also this size (small) is the perfect fit for our small staffy who is a bit leaner and less stocky than the typical staffy.