OK, let me clarify this one.  Up to this point there have been many companies who use chemical milling to manufacture thin metal components, and there are also companies who use etching to produce thin metal components.

So what is the difference?  To be honest, there really is no difference.  Photo etching, chemical milling, chemical etching, etc are all the same thing.  The difference comes if you look to chemical etch versus electro etch, a story for a different day.