I seriously wonder though how 'active' they really are. Some just have a strand in there that is connected to one of the batter terminals, nothing more, certainly not an active part of an RLC circuit connected to the cable.
But then, I have not seen their schematics either on those that do claim active roll.
And, how in th eworld the designer knows what frequency needs an 'active' interfernece and to what degree? Just more smoke and mirrors parlor tricks