If the Graphite block can pass enough current to trip the breaker, and does not fail itself, then it can be UL listed. It would have to be tested by Underwriter's Laboratory.
How much it improves sound, and whether one chooses to spend $3200.00 on it is another matter. I wish the original review here, included a listening evaluation.
Not to be too critical here but note that Underwriter's Laboratory (UL), does not "approve" products. This would make them liable for lawsuits in the case of shock or worse. They only run tests on products, and "list" them if the product passes the tests.
You might want to re-read that- I never wrote "UL approved", I wrote "UL
listed", which is all they do, after their safety/destructive analysis testing.
Also, the only part of the circuit that passes through the graphite block, according to the description, is the ground. How that will cause the breaker to trip, assuming everything is OK, I don't know.
The problem still exists- companies and people making things that are described as wonderful but not having any ability to do what they say. There's nothing in this device that would improve sound quality. The housing being made of an expensive aluminum alloy? Really? $3200? GMAB!