The statement on their site reads: “A substantial number of face masks, claiming to be of KN95 standards, provide an inadequate level of protection and are likely to be poor quality products accompanied by fake or fraudulent paperwork. These face masks may also be known as filtering facepiece respirators.”
As a result, KN95 masks must not be used as PPE at work as their effectiveness cannot be assured.
KN95 is a rating issued by the Chinese standards for face masks and is broadly the same as the European requirements. However, the quality of KN95 masks is not independently certified - they’re declared safe by the manufacturer.