I should have noticed that these cables are only 1.5m, whereas normal ones are 2m long - so these are a bit short. My fault - but do be careful.
However, they are rather carelessly moulded - the pins are not placed in the centre of the plug, and consequently will not plug in without some persuasion with a screwdriver to lever them centrally. Quite a few people will not be able to manage that.
I'm not sure of the value of the ferrite cores; but they work well enough!