DIFFERENCE BETWEEN ONE ARM and ROUTED DEPLOYMENT OF F5?

Correct. Additionally, the "arms" used to be typically referred to as physical interfaces. Prior to 802.1Q, IP addresses were allocated to single interfaces. In actuality, "arms" refer to VLANs with an associated IP. You can have a one armed config with more than one physical interface. You can also have multiple one-armed configs with more than one VLAN on the same BigIP. But the implication would be that the interface which the vlan is associated to will be used for both ingress and egress traffic. If that is an LACP trunk, then traffic will get hashed and distributed on the trunk.