What Mike said. The majority of the stuff they flog to home users is "pikey duplex" as Mike puts it.
"HP Photosmart" sounds like an inkjet. I'd personally stay clear of attempting duplex on inkjets unless you're really insistent, and even then, you'll need to be using half-decent substrate, not toilet paper to print on. But each to their own, if you're happy with the results you're getting, so be it.