Each kit has some moving mechanical components to it. The little fidget kits have a gear to spin around, while the stagecoach has opening doors, boxes, and can move on its own after a few twists of the winding key. 

The kits can take anywhere from 10-15 minutes for the simple ones up to 16 hours or more for the more complex ones. 

If you don't use the easy-to-follow step-by-step instructions, they can be turned into a challenging puzzle as well!