Because a drawer opens where it stands, so its contents stay accessible regardless of where the unit sits in the stack. A lidded box at the bottom requires unstacking everything above it. Drawers therefore suit constantly used tools, and lidded boxes suit tools taken out once per job.

Drawers for hand tools, drivers, blades and consumables retrieved many times a day. Lidded boxes for machines and job-specific kit taken out once and put back. Reversing this is the usual reason a modular system feels slow, since the frequently used items end up under the least accessible lid.

An organiser is a shallow compartmented case, generally with removable bins, aimed at fixings and small parts. A drawer unit is a stack component with one or more full drawers for tools. Many users run both - organisers for consumables, drawers for the tools that use them.

They let a subset be carried to the work rather than the whole case, which saves repeated trips back to the stack. Combined with a clear lid, they also let the right bin be identified without opening anything, which is a significant part of what makes an organiser faster than a compartment tray.

The runners. A drawer loaded with steel and opened on an uneven van floor or a sloping site puts high side loads on them, and worn runners bind and eventually jam. Runner quality and load rating are worth comparing directly, since they are the difference between units that otherwise look identical.

Only if the unit lacks a positive retention catch, and then they will - a stack that shifts when a van brakes can empty a drawer across the load space. A catch that has to be released deliberately, rather than friction alone, is the specification to look for.

Within the same manufacturer's system, yes - that is the point of the shared interface, and drawer units are designed to latch to the same boxes. Across systems, no. Check that the drawer unit's depth suits the stack height you actually load into a vehicle, since drawer units are often deeper than basic boxes.