Dual Voltage Units usually input high voltage and output high voltage AND 120volt with help of a transformer. Most do NOT allow for connections to subpanels which require 4 wire outputs.
Some Dual Voltage units can output 4wire 120/240v for subpanel needs. Look for units with Isolation transformers.
Finally some Dual Voltage units (called Split Phase) require 4 wire 120/240v input and output 4 wire 120/240v for transformerless dual voltage needs OR connections to subpanels. Look for units with L1430 (4wire 120/240v) outputs