I am being talked about in reference to distortion in wire, etc, so I might try to clarify things. First, I have measured cable differences, especially at low operating levels, that I would not normally expect. While, statistically I might find that cheaper cables like RS measure worst, it is not ALWAYS the case, and some wires, that start badly, seem to break-in with time and signal, and measure better. I think that a fuse is so nonlinear in nature, that it would be almost impossible to measure fuse 'directionality' without laboratory conditions and a good deal of computer time.
Since fuses are supposed to heat up, I'm not sure how they could ever be linear, I don't know of any material that doesn't change resistivity when it warms up.
And a fuse that doesn't warm up isn't a fuse.
I don't doubt that some wires have distortion, by the way, but when I see it, there usually seems to be some very dumb connector, or a level of cheapness that would make Mr. Tandy wince.