It's wonderfully whimsical, the visual impression delivered by the Stacking Shelves. They look to be different pieces of furniture piled up into various off-hand arrangements, when really they're quite secure in most ways that you might join them.
The key is to ensure that the turned wooden legs of one unit are matched up with the divots in the upper surface of the module below. No hardware is necessary to stabilize these connections, but you can be sure that the configurations that you create will look and be well balanced.
The Duffy London furnishings come in wide and narrow versions in different timber stains, functioning beautifully as individual tables and combining into elaborate and playful storage systems.