Digital isolation between Ethernet hub and streamer

As far as I can tell, these filters provide galvanic isolation in one of two ways, by either using transformers (i.e., the NA filters) or optical isolation (i.e., GigaFOIL and others).  Don't most good servers/streamers also provide some form of isolation?

The last cable my streamer sees is a fiber optic cable but, even when it was an Ethernet cable, none of this stuff made a reliably discernable difference in the sound of my system, and I have owned the NA eno and muon systems (including their Ethernet cables), GigaFOILv4-INLINE, and others. I could say I heard differences, but that would require talking myself into it, YMMV.

I have the Network Acoustics (NA) Eno2 'Ethernet Filter' system with the NA LAN cables (the cables come with the Eno2 as a package deal option) and it made a significant difference immediately noticeable in soundstage dimensions, image clarity and instrumental separation. The science behind devices like these is readily available on the internet. More importantly, in a higher end system devoted to digital sources like mine, the devices simply work their magic, and apparently for many others as well.

I just don't get why, BEFORE open-minded experience of these devices in one's own system, one would discount their efficacy.

They work for some and for others not so much. Kind of like power cables and the like.  Don't be a binary thinker (cuts both ways) and just disqualify the product or people's position on that given product, positive or negative. 

I always like when somebody posts “This very inexpensive”.   It’s typically not “very inexpensive “ to me anyway’s.  When someone says to ME very inexpensive I think $20-$50US.  Not over $200US. Thats more like a, well let me look into it, and think about it.  Inexpensive is when I think, hum, $30-$40, I’ll try one out.  At $200 there’s a bunch out there and I already have plenty of that kind of thing.  
Of course, some people‘s idea of an expensive is different from other people’s idea of inexpensive.  

I have tried:

1. Network Acoustics Eno Streaming System. Did it do something ? Yes! It smoothed out dynamics, tamed the highs and relaxed the mids. Soundstage collapsed. None of the effects were desirable and I sold it

2. Fiber optic conversion - adds glassy and cold character. Didn’t mike it

3. iFi LAN iSilencer - made zero difference or if it did make a difference I can’t hear it. Because it does no harm I left it in my system 

Other than using the best possible Ethernet cable and keeping your network components out of your system and plugged into a different circuit, there’s nothing else to do with Ethernet.