Hi,

Below is an instruction you can refer to: 

https://www.tp-link.com/en/support/faq/2248/

Comparing the difference between M5 or M4, the option 2 seems better.

https://www.tp-link.com/en/support/faq/2423/

While cause the performance is affected a lot by the actual network environment, you can try different options and find the best one.

May it help and have a nice day. 

kkumul wrote

I have 2 M4 and 2 M5.

the main unit is M5 and other 2 units are on ethernet backhaul but 1 unit has to be wireless.

 

I don't know which Deco should be wireless. M4 or M5?

 

option 1:

modem -(wire)- M5 -(wire)- M4 -(wire)- M5 -(air)- M4

 

option 2:

modem -(wire)- M5 -(wire)- M5 -(wire)- M4 -(air)- M4

 

option 3:

modem -(wire)- M5 -(wire)- M4 -(wire)- M4 -(air)- M5

 

Which option is the best?