If substantial batch-level or product-level costs exist, then overhead allocation based on a measure of volume such as direct labor-hours alone:

is a key aspect of the activity-based costing model.

will systematically overcost high-volume products and undercost low-volume products.

will systematically overcost low-volume products and undercost high-volume products.

must be used for external financial reporting since activity-based costing cannot be used for external reporting purposes.