Packet flow explore for main route metric order
ZyWALL 110 on V4.33(AAAA.0)ITS-WK30-r89425
From the help listing
“This option appears when Interface Type is external or general. Enter the priority of the gateway (if any) on this interface. The Zyxel Device decides which gateway to use based on this priority. The lower the number, the higher the priority. If two or more gateways have the same priority, the Zyxel Device uses the one that was configured first.”
I set OPT to metric 3 and VLAN443 to metric 1 the order in packet flow explore for main route shows OPT at the top of the list.