I bought this product for listening/recording music on my macbook with my headphones (Beyerdynamic DT-880) which has only a 6.3mm jack.
But there was a bad contact in the 6.3mm jack bush. Fortunately, I could repair it with an endoscope (which of course is not a common tool you can find in every household). The problem was a misaligned (bent) contact inside the jack bush. Even the quality of the components looks to be very good, there are 2 possibilities for the failure:
-bad quality check at the manufacturer. However, the quality of the material looks too expensive to have been produced by a cheap manufacturer in China.
-the jack adapter was a customer return (most probable reason, as the package was open)
Of course I could have sent the jack back to thomann, write a bunch of emails and wait for a replacement, but I decided to check and repair by myself. On the other hand, I had no time for waiting and I expect a functional product - considering it is a really "basic" product.