In the US, all domestic plug-in equipment and appliances are designed for 120VAC.
The wiring installations in residential and small commercial have been 120/240 volts, using two 120 volt legs and a earthed neutral. The 120 volt legs are 180 degrees apart and used together produces 240 volts for large loads. This practice has been in use for at least 80 years.
The only reason I bought the transformer is because it was cheap and it's a interesting conversation piece.