Now that you mention it, yes, the branded eye piece does taper a little bit different than the sussex. And it's made of plastic. My sussex is metal (aluminium?)
The unbranded eye piece feels like metal, but it's so tightly screwed on I can't get it off to check. It does not have the same lip and is completely smooth all the way back. The lens is screw in as an inset, rather than a "add on", explaining the lack of that lip. The windage knobs also seem to be positioned circa 5 mm further towards the front of the scope (the unbranded end).