I can't see how any fuse running within it's rated current capability could have any effect (detrimental or otherwise) on the sound.
At the end of the day, it's a (very, very short) piece of wire, designed to snap when it's rated current is exceeded.
To my mind, the most crucial part, is the contact area between the fuse and fuse holder, and unless both items are gold / gold plated, I fail to see the point of gold plated contacts. I believe that it would in fact be better to have a fuse with brass end caps, unless you happen to be using a plug with a gold plated fuse holder..
And all the plating - "gold over silver end caps" and "pure silver wiring"..... There surely has to be some compromise in electrical conductivity with all this plating...
Also, the seller of this fuse states "ceramic casing, rather than glass, for better resonance characteristics" - well don't
all UK mains fuses have ceramic bodies? And as far as I know - ceramic bodies are used because of their superior non flame properties - glass fuses have a tendency to shatter under circumstances of extreme failure. And resonance? In such a small device, which is passing 50hz mains? That did make me laugh...
My suggestion? Stick with the 20p fuse you can buy in the shop, buff up the end caps with a bit of 400 grit sandpaper, clean the fuse holder in the plug using the same method, and save yourself £25 !!
Pass me another can of snake oil please!!!
Tony.
P.S. and as another poster pointed out: 13A is overated for most Hi-Fi kit.