https://www.amazon.com/gp/product/B07SHLS639/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 I just bought this one because I got tired replacing the 9V batteries, so far it is very accurate, specially when test capacitors.

Ferrum support was smoking something, it is their fault to choose such odd ball socket. It is NOT the fuse sound REALLY bad then backward, they sound little artificial, awkward (unnatural), and MAY gain some dynamic and have wider soundstage when backward, yeah it is funny.

How ever this is correct:

Like this:

The direction in the pic/drawing above is backward

If your system has 6 or more fuses, it is very hard to single out each one before you get really mad, sad, or just want to kick something!! I been there, just before I tired to kill myself, I took one step back look at the "industry standard" that is if you look at the fuse facing the logo...

If the system is detailed enough, people will tell the difference, but the process is slow, the ears might adjust to the sound already that make it hard to tell. I had my preamp ordered new and listened it for a few days, then I hooked it up with a CDP, took the bottom cover off, placed a fan...

You have to play music or noise to let some current flow through the fuse to burn in, all the fuses I have their sound improve pretty linear.

PM

If the fuse is installed in a wrong direction, the sound will be odd. If the fuse's direction is not marked like Hi Fi Tuning, the general rule is look at/face the name and lettering, the direction is from left to right.

Rattling is OK as long as they sound good, also there is nothing you can do about rattling.

Used Synergistic SR20 when they first came out maybe 10 years ago, anyway, it was a long time ago, the fuse changed the image shape and sound stage too much, the music flow was not natural.

It depends on your system, I am still using the old AMR gold fuse, Created Audio, and Gold Hi Fi Tuning, never seen the needs to replace them, I am really careful not put N th degree of details, wide sound stage, sharp/clear leading edges, and…… the list is long into my system, I have enough...

Sorry I can’t remember that was a loooooooong time ago but I can tell you that use 6SN7 instead 12AU7 family tube is a generally a good direction. Change the coupling caps or bypass them with something like jupiter copper foil caps is a cheaper and more effective way to improve your WA22 instead...

Well, GL used to be $200 a pair, now WE300B replicas by PSVane and LindaI are both over $1000 USD and for $500 more you got US made Rossville WE 300B replica beaters......hum.....all don't make too much sense anymore.