Update: the seller will refund the price, I'll have so there are no functioning new devices for evaluation.
Have, however, the first two defective equipment screwed and very quickly discovered the reason for the non-functioning: the connection cable was simply not soldered to the controller board. Not bad soldered, but not at all. There were not even the cable ends stripped. Freuts me, I can do with relatively low net expense the parts done here now, but as something to be sent is beyond me.