Like Old Jeep says there is a big difference between 110V operation and 230V operation.
Here's the specs for the Millermatic 211: 115Vac, Amp. Range 30 - 140, Rated Output 90A@20V@ 20% Duty Cycle
230Vac, Amp. Range 30 - 210, Rated Output 150A@23.5V@30% Duty Cycle
If you are looking for portability the Miller PassPort Plus is a really nice unit, even comes with a gas cylinder.
115Vac, Amp. Range 30 - 140, Rated Output 110A@19.5V@20% Duty Cycle
230Vac, Amp Range 30 - 180, Rated Output 150A@21.5V@20% Duty Cycle
Both welders can do: mild steel Min. 24ga. to Max. 3/8"
alum. Min. 18ga. to Max. 1/4"
Aluminum should be done with the optional spoolgun.
Any welder or plasma cutter that is dual voltage should always be run on a dedicated circuit with a 20A breaker.