You're correct Harlan, most of the budget priced "C" presses are made in China -- regardless of who sells them in the US. The debate usually centers on whether the same manufacturer(s) makes all of them, and whether or not they are made to the same specifications. I don't know one way or the other, but have handled the Astro set, the old HF set, and the Powerbuilt set. Superficially, I can't tell the difference -- they look/feel the same. I always lubed the press screw on my HF set with anti-seize and never had an issue with stripped threads.
The Master Kit add-on from HF was a good buy because many folks purchased the higher end tool truck and OTC press sets, but found that the receiver cups and pressing discs in the HF set were good enough for most jobs --- versus purchasing the very expensive expansion kits from the tool truck.
As you stated, the Master Expansion kit alone is also a great choice for making a standard hydraulic shop press much more versatile. In fact I use the cups and discs much more with my hydraulic press than the "C" press.