I am worried that there is not really a benefit of doing that, just more noise and energy consumption.
This is not the way to do it. The correct way would be multiple SSID’s with each tagged to their own VLAN.
Each VLAN has its own subnet. You can then use a zone based firewall, to allow the zones(subnets) to access each other.
You can also then apply QOS, to limit guest network speeds, prioritize LAN traffic etc.
And zone based firewalls are stateful, you can do rules such as LAN can reach IOT, but not the other way. Or IOT can only reach the IOT server, on specific ports.
I know that this would be the most secure way. But I seriously doubt that this level is necessary in a normal home network.
“Necessary” is a little ambiguous. You could argue that wifi is unnecessary for a normal home network.
Well, I think it is necessary if you have mobile devices. Anything nailed down should be connected by wire, but if it is mobile, it should get the connection. Especially if the cell phone link is not that good inside the house.
None of my mobile devices are “necessary,” though. Honestly, I could live just fine without an internet connection. Not that I’d enjoy it, but that’s not necessary.
My solution is the correct way and easier way. You don’t need MAC address white-list. You just have a guest SSID with DHCP on, they get the IP from the subnet in that zone. No crazy subnet hacks etc.
Can I join your guest network, sure. Let me just grab your mac address, login to the DHCP server, create a reservation with a limited subnet mask that can still see the default gateway.
Or can I connect to you guest network, sure here is the code or scan that QR code. That’s it, they’re in the guest VLAN and subnet, zoned off on the firewall and have QOS applied to not saturate the network.