@Jebster 

I own Deco mesh, with M9 Plus units, and can confirm that Satellite Deco Ethernet ports can be used to connect wired devices.

One of my Satellite Deco is used in the following network setup:

ISP modem/router- switch - Satellite Deco - network printer connected to Ethernet port

Two things to mention:

1. You do not need to pass all network traffic through Main Deco if you plan to keep your existent router. You can configure Deco mesh to run in Access Point mode and that will increase flexibility in how you can wire your Deco units to home network. More about Access Point mode here: How to set up Deco to work in Access Point mode

2. Not every switch is compatible with Deco Ethernet backhaul. More on that topic here: General questions about Ethernet Backhaul feature on your Deco

  @Alexandre.  Thanks for the answer and how you have your setup.  But to me that isn't two Deco M9 connected with a main and satellite.  So I'm still unsure if it will function as I would like.

The information on Ap setup was very useful.

thanks Jolyon 

Jebster wrote

Hi All

I'm looking at purchasing a Deco M9 mesh setup. My house has Ethernet cabling and a switch just poor wifi signal that I'm try to improve. I want to use the backhaul setup below 
 

ISP modem - wireless router- main Deco - switch - other Deco - TV connected to Ethernet port. 
 

I have seen it's possible to connect a device to the Main deco using the Ethernet port, but can anyone confirm if you can connect a device to the satellite Deco Ethernet ports. 
 

  @Jebster 

This will work. You can connect a device to the satellite Deco Ethernet ports.