Does air-dry clay actually hold up after it dries?

It depends on the brand and the project. Reddit threads in r/crafts and r/ArtEd repeatedly note that lightweight kid-grade air-dry clays can be brittle and aren't suitable for anything that takes abuse — for durable pieces, hobbyists recommend oven-bake polymer clay instead. For decorative figurines and school projects, the kid-targeted kits are fine.