The only difference is if you want to use the Ethernet ports, the e4 port is fast Ethernet 100mbps max and the d4 port is gigabit Ethernet 1000 Mbps max.
So it depends on your subscription. And above all whether you want to use the ports (for example connected directly to a PC) or just the wifi.

You can still operate the M4 in "extender mode" if the mesh network does not work as desired. With the E3, only "router or access point" is possible

If you employ a Giga Switch, make sure you use the M4 with 1000 throughput!
I am very satisfied 😉👍