What's the difference between a vest with iron-sand pouches and one with removable iron plates?

Iron-sand or ironsand-pouch vests (common on budget ZELUS, Zeerun and VEVOR models) tend to be flexible and low-profile but offer coarse, fixed weight steps. Plate- or block-based vests like the Eric Flag (2.4 lb iron plates) or CAP (stackable bars) let you fine-tune the load and generally distribute weight more evenly, which specialist calisthenics threads prefer for heavier training.