Hi
Some excerpts from the following KB.
https://documentation.meraki.com/MX-Z/Networks_and_Routing/Addressing_and_VLANs#Addressing%26VLANs-P...
In this mode, the MX device does not provide any address translation and operates as a passthrough device between the Internet and the LAN ports (sometimes referred to as a Layer 2 bridge).
ALSO
Placing an MX appliance in Passthrough mode at the perimeter of your network with a publicly routable IP address is not recommended and can present security risks. As a best practice, Passthrough mode MX appliances should always be deployed behind an edge firewall.
Regards,
Ajit
AjitsNW@gmail.com
www.ajit.network