You may rely on the quality and safety of this German made belt 100%:

The manufacturer of this extension produces original safety belts in all accordance to the regulations and rules of the Federal Automobile Agency, Technical Inspection Agency and the German Motor Vehicle Registration Agency.

Furthermore, they have been inspected and certified by the Motor Vehicle Registration, in accordance with the DIN EN ISO 9001 for production and manufacturing of safety belts and safety belt components, in accordance to all national and international rules and regulations for road traffic.

The extensions have been "TUEV" inspected (by a federal inspection agency, authorized and certified as such) and certified as safe, in accordance to the ECE-R 16.