Can this device be installed in an installation and comply with B.S. 7671?

I cannot see anything wrong with the device, but I cannot really see many applications either. A typical one which may come to mind is an EMC test enclosure (cage) with mains sockets and an operative inside. However the solution to this is simply to put the RCD after the very high attenuation mains filters used for such an application, which may pass considerable current to Earth, for additional protection and to meet BS7671 "socket outlet" regulations. I can see very little reason to fit one to VSDs, because they do not usually drive socket outlets, although there may be a case if the supply is TT, but 30mA protection is very unlikely to be required. The question is probably whether the device adds risk under the proposed use, or reduces it. The fact that it doesn't reduce 50Hz "leakage" suggests that its real purpose is to reduce possible EMC cases with certain types of VSDs, but if so it is probably well behind the design curve of modern power factor corrected drives.

I cannot see anything wrong with the device, but I cannot really see many applications either. A typical one which may come to mind is an EMC test enclosure (cage) with mains sockets and an operative inside. However the solution to this is simply to put the RCD after the very high attenuation mains filters used for such an application, which may pass considerable current to Earth, for additional protection and to meet BS7671 "socket outlet" regulations. I can see very little reason to fit one to VSDs, because they do not usually drive socket outlets, although there may be a case if the supply is TT, but 30mA protection is very unlikely to be required. The question is probably whether the device adds risk under the proposed use, or reduces it. The fact that it doesn't reduce 50Hz "leakage" suggests that its real purpose is to reduce possible EMC cases with certain types of VSDs, but if so it is probably well behind the design curve of modern power factor corrected drives.