Whoever said that two of these could not be stacked did not read the instructions.  Stacking two of these takes up the same amount of space as the Classic 24 bottle spice storage rack while providing more than double the storage in the same space.  Another aspect that I really like about this system is that all the spice containers are the same size so I don't have to constantly move bottles around to accommodate all the different sizes.  And even if I do have to move the containers around because of new spice, these can be easily removed from the carousel and placed in a different spot without having to worry about it fitting.

Pros: Same sized containers for easy storage