Make a decision
Airflow test versus duct vacuum
One scope
Airflow or static-pressure measurement can expose restrictions and fan performance issues.
The other scope
Vacuuming removes debris from an identified duct section under containment.
A concrete example
A cold upstairs bedroom may have a poorly designed return. Vacuuming a clean branch will not change its dimensions; measured airflow can guide the next decision.
Which question settles it?
If rooms remain cold, cleaning alone is not a test of duct sizing or balance.