That’s similar to the isolated vlan but someone who knows more about networking than me will probably be able to explain why the vlan is superior. I would imagine it’s failsafeness, the vlan is just its own thing

The benefit of doing the domain specific firewall blocking would be if you wanted your printer to otherwise have internet access (eg to check octoprint remotely). I don’t print when I’m not home due to the risk of fire and I don’t trust opening up my printer to the web, so I don’t bother with this. Others may have different opinions on acceptable risk