I absolutely love them! I also think that, as an adult, it's totally fine to wear a backpack if you want to. Especially if it's as cute as these ones.
All of my handbags are usually super heavy, as I carry around tons of stuff wherever I go. Having a backpack like this would really help my shoulders out because the weight would be balanced. Plus it has a bunch of pockets to keep things organized.
The backpacks come in a bunch of different designs. I love the one pictured (pastel blue floral). That particular pattern costs $44.50. Depending on the design you like, the price ranges from $39.50-$79.50.