Can and do they work? Yes, of course they do just like wireless and cellular does on your phones. That said, as with every type of wireless adapter, they will never be as good as a physical cable. Signal will be degraded by walls and ceilings, how much so will depend on your wall/ceiling construction. Other Wi-Fi or radio signals can cause interference which will degrade quality. Quality and strength of the units you're using will also affect the ability to use them in your environment. You can read the reviews of the items listed in your link to see they're hit and miss and as I mentioned, there are many variables. I would never recommend them over a physical cable, BUT, they can certainly work for those situations where cabling is just not an option. I wouldn't expect a perfect cable like 4k experience all-day every-day however. You'll likely have to buy and try in your environment to see if they work in your application.

You have to decide on aesthetics vs. likely service quality.

That said, you could bundle your wires in colored wire loom or mesh and they become much less of an eye sore. Run behind base trim or through the walls to make them even more hidden (where possible).

Like Steve J mentioned - if at all possible get a wire from point 'a' to point "b".

However, I've had success with one product from Gefen. We had a situation with a TV over a fireplace - 18 foot cathedral ceiling, concrete slab floor, it was a newly built home and client said no way, no how to cutting and patching walls or ceilings (even if we could).

We used a wireless product from Gefen (link below) with good results. The distance was fairly short between the cable box and TV, I would say about 15 feet line of sight. Res. is 1080, not 4K (it is what it is). Worked well. Device transmitter also has other HDMI inputs for additional source devices. And although we tested this device between floors (and it held up well) in different environment, I would still be a little cautious using this device between floors. If you can purchase from a reliable seller - meaning that they'll let you return it if does not meet expectations, then go ahead and try it. Priced around $350

http://www.gefen.com/product/wireless-extender-hdmi-long-range-EXT-WHD-1080P-LR

I/O GEAR also makes these products, but I haven't used any of then so I can't speak to the quality.

https://www.iogear.com/product/GWHDMS52MB/

Good luck with your project

-Frank

Not understanding this convoluted q from OP.

For audio-only, go either wired (via the ridiculously low tech and perfect option of direct speaker wires) or wireless.

For video[+audio], that's a different topic entirely and unfortunately.

Steve, wireless HDMI is a niche and dying technology, although its lifetime may be within the OP's usefulness horizon, and it is overkill for a purely audio application.

Where is OP asking about “purely audio”? And I suspect English is not the OP’s first language.