Are stackable shoe racks stable when stacked tall?

Verified-purchase reviewers say stackable metal racks are generally stable up to two or three units high if anchored on level flooring, but commenters in r/Vans note that older plastic or thin-wire units get wobbly over time. For towers above 6 feet, reviewers prefer single-frame tall units like the SONGMICS 12-tier over independently stacked modules.