that's what they advertise it as, 4 streams to lan devices over wifi. No clue what 4k you're watching but 20mbps is barely enough to get good 1080p, standard 1080p is around 12mbps for video alone, and depending on audio it can go up to 40, each. 4k hdr is 80mbps video alone, and majority of them are also truehd 7.1 which will make it over 120mbps. the "upto" sounds very much like a you might get 4k output on one screen but multiple it'll do 1080p at most, assuming you get good OTA signal.

only way around that is either compressing it to shit (why even bother at that point) or interlacing it which is how it's been done so far, to again reduce quality drastically.

and again, 1gbps nic and controller will cost manufacturer literal pennies to use instead of 100mbps and if it's already being manufactured in china it'll cost even less as they're abundant. The only reason they'd go with 100mbps is either because design spec is old af or they genuinely believe 1gbps is somehow a hindrance.