Any visible wifi network is bound to get attacks and WPA/2 crack attacks, which is an attack vector into your home or office network. Especially since OpenWRT is set up by default as an access point, which forwards traffic to the wwan network, i.e. your main network.
I've set up firewall rules for the VLAN my iot devices are on, but still, less than optimal.
Would you rather have an extra door or a solid wall in your bank vault?