Hi there,
I am currently using an AVM Fritzbox 4040 router and two AVM Fritz 1750e repeaters. Unfortunately, AVM Fritz routers cannot use VLAN. Now I have seen that it can install openWRT for the AVM Fritz 4040 and also the AVM Fritz 1750e Repeater.
Before i do this, one question first 
AVM Fritz products use the Mesh Wi-Fi steering LINK
So I connected the two Repeater 1750e to the Fritz 4040 router over a LAN cable.
Can then integrate the two repeaters into the Fritz Mesh.
Now the two repeater automatically adopts all settings from the router
If I change for example the WiFi password, all repeaters in the mesh automatically have the new password immediately.
Or if i change the SSID in the router, both repeaters also have automaticly the new SSID immediately
etc...
Is that also possible with openWRT?
I hope I was able to describe it clearly, sorry, my English is not so good 
Thanks