Since unbalanced audio gear almost always connects signal ground and chassis/safety grounds together, this box provides no isolation at all, or any cure for mains/ground loops.
Hifi gear even having safety grounds is a relatively recent thing/trend
I have/had many Amplifier, caste tape decs, CD player and turntable with only 2 pin plugs.
So in this case yes a isolation transformer can help lower mains leakage and captive coupled ground loops trough mains and/or neutral.
this is especially noticeable with low power signal sources like turntables and not noticeable with high power signal sources like DACs.
Oh and that the AP Analyzer input is maybe better in dealing with common mode current/noses then the average Phone preamp/AVR
shuld also go without mentioning.
Even if it would be like you say that only balanced gear has it’s signal ground not directly safety ground referenced...
Many users use speakers/amps with balanced inputs but with unbalanced cables/sources.
If I wanted to see the general impact it would have on the quality of my audio system I very much would so thank you for the review.
They are not used/marketed as universal improvement but as a fix for a specific problem.
in the audio world this would be common mod currents and "hum".
You don’t take pain killers if you have no pain and expat to feel better.
(Well maybe that's a bad example considering Opioid abuse... but you get the point)