Radius is a Japanese company, and as far as I understand they own a factory in mainland China which means they dont use any OEM manufacturing, an example would be Brainwatz or Fisher Audio, which orders to a large OEM factory to make they earphones.
In recent years Radius quality control has increased because there is just no way they can do otherwise, japanses customers will not tolerate any quality issues.
in 2012, 4 years ago, Radius faced issues with the THW-21 IEMs. for those who dont know, this was companies 2nd flagship released after the TWF-11,
So Made in China does not mean quality is worst then if it was made in Japan.
Only few IEMs manufacturers are making earphones in Japan today, such as Ortofon, JVC, Flagship model from Final and Sony
as well as Fitear and other few other 1000+ headphones from Audio Technica and Pioneer.