The mode of the MX is necessarily determined by its purpose (use case). Therefore, I think it is best to avoid discussing the superiority or inferiority of each mode in a myopic way.   To benefit from the redundancy provided by DC-DC Failover, it must be a One Armed Concentrator. Therefore, when redundant Primary and Secondary DCs are used in a corporate network, the DC side must use the One Armed Concentrator.     Datacenter Redundancy (DC-DC Failover) Deployment Guide - Cisco Meraki   https://documentation.meraki.com/MX/Deployment_Guides/Datacenter_Redundancy_(DC-DC_Failover)_Deployment_Guide   Routed Mode is suitable for accommodating Internet connections at branch offices. To put it another way, One Armed Concentrator cannot accommodate Internet connections. ... View more