My impression so far is there is a very subtle improvement in tone (slightly smoother highs and a bit tighter bass) and separation of instruments.
I have a DH Labs ethernet cable but it’s coming directly out of a Cox cable router and I am sure that if I used an optical or other decent switch it would make zero difference.
I’ve ordered a SmoothLan and will compare.
Lastly, I had no expectations but it is a zero risk tweak that I can return and then say it did or did not work for me in my system.
Even if you are skeptical, which everyone should be really, you could start by understanding what these products "claim" to do - which in this case has zero to do with recovering lost bits.