Daz,
Wow you are correct, I just said that because they have a link to the Mach4 USB plugin but it has this message attached. Good think I got the ESS version.
Russ
Mach4 Plugin for the USS (USB SmoothStepper)
May, 2016: There is not a Mach4 USS plugin. We are about to officially release a new Mach4 ESS plugin, which will be the basis for the Mach4 USS plugin. We expect it to be released summer or fall 2016.