Most companies set up manufacturing in other, cheaper countries in order to keep the labor costs down. This saves the consumer on the cost of the final product. In most cases the product, regardless of where it is manufactured, is subject to the same quality controls of the main factory (parent company).
For years, I worked for Philips Lighting in the Halogen and Automotive divisions. We produced lamps for Bosch, Stanley-Europe, Hella, and a few other top-name companies.
Unless someone else has insight on these plugs, I would trust them as I would the ones made in Germany.
Just my $.02
76 240D (W115) - 550K miles
78 300D (W123) - 200K+ miles