There are only two genuine smoothsteppers, the original USB SS and the newer Ethernet SS, both produced by Warp9TD.
Anything else that happens to mention smoothstepper in the name (i.e. quite a few ebay listings), is not a smoothstepper. I think PMDX are official resellers, so if you go for a PMDX BOB, it'll most likely be worthwhile getting the SS from them at the same time, to reduce the number of customs handling fees you'll need to pay.