My experience in replacing my 3A Buss fuse with a HIFI Gold Tuning fuse is the complete opposite of all of the hype out there.
I have two systems, each supplied by an Allnic L3000 Mk2 preamp either feeding a Tube Audio Lab 300b amp to Yamaha NS1000s or feeding a Tube Audio Lab 2A3 amp to Omega Alnic XRSs. The test consisted of swapping the fuses while leaving every thing else the same such as volume and turntable source.
In both instances, the stock fuse sounded much better by a long shot. It was not subtle, I can hear the difference withing 30 seconds after a needle drop.
The HIFI Gold Tuning fuse lessened that special holographic 3D mid range associated with SET amps. The music sounded recessed and more ordinary. It did not change if I switched the direction the fuse was inserted. Granted this was not a blinded trial. In fact, I was rooting for the HIFI Tuning Fuse given the stupid money that I paid for it.
I would encourage that you try one out in your system yourself. Listening is believing. I might try in other equipment; otherwise, I have a used HIFI tuning fuse just sitting around. I wondering if it will fit in my Hickok tube tester?