The Duo is essentially a LabelWriter 400 Turbo mounted on top of (and nicely integrated with) what amounts to one of DYMO's LabelManager printers, which print on plastic.

How to Configure a DYMO LabelWriter to a USB Port. The DYMO LabelWriter series of thermal label printers enables you to address mail and packages, print postage and identify business projects ...

The Dymo LabelWriter 450 Duo combines two printers in one case, with both a printer for paper labels and one for plastic labels.