In the measurements I’ve made, they only seem to show up with equipment that actually draws enough power that you can measure a voltage drop across the fuseholder.This is "maybe" a correct statement, but lets get the rest of it right, and may only apply to non regulated equipment.
What should be added is that it would be "impossible to hear" the difference. As the mains fluctuates much more every second, your measuring the same ***** thing, a minute voltage drop across the fuse or larger voltage drop in the mains every second!!!
It’s all fuser snake oil voodoo **, don’t try to make it anything else and give fusers even more fodder for the shilling of these >$160 fuses
Cheers George