They begin as a slip and that is where their interest: their use for this transitional period during which small are not 100% sure. They can stand alone and remove their beds and then recover after pee, without necessarily calling Mom or Dad. Plus: a sign indicates the child the front and back of the layer to facilitate the installation.
Also note that the only differences (visible) between layers for boys and those for girls are the color and the small symbol indicating the front and rear.
These layers are transient security, but remain optional depending on whether the child gets up alone or not during the night. If he calls his parents or if it is in the layer, it is perhaps not necessary to spend (much) more money for the same use than a basic bed for the night, and therefore much cheaper!