I played around in lab with a Z3C-NA for a specific POC requiring dual internet.
Indeed you can convert the Port 2 to "Internet" same way as MX64/67
However, you will not get the exact same behavior / redundancy level than with MX64
On teleworker gateway, you don't get the SD-WAN menu so no option to set active-active VPN on both WAN Ports or load balancing features.
In definite, it is basic but it does the job to connect two WAN circuits in addition of the cellular function.
Totally absent of the documentation, i'm not sure it was Meraki intention to provide such feature on Z3C



