@Alexandre. Thank you. I was looking at the AV1000. Could you explain the difference between the "Kit" and the other? 
Also, is the AV1300 similar but just 3 ports as opposed to 2 ports? Thanks again!

  @Alexandre. Thanks very much. I appreciate your help. 

  @Goatboy 

In unit name, AVXXXX means theoretical possible speed over powerline link. For example, AV1000 promises gigabit speed, but in theory. In practice, over average electrical wiring from and average house expect about 60% of promised speed at most.

From the other hand, faster powerline adapters are more sensitive to interference. For example, while AV2000 might deliver actual gigabit speed, it is possible it could briefly drop connection completely when you turn on microwave, while AV1000 or AV600 may just reduce speed while microwave is running but keep connection.

So, you choose between speed and reliability. AV1000 sounds like a good compromise. 

  @Alexandre. Hey one other thing. Do him think the TL-WPA7617 KIT is a similar kind of thing EXCEPT it is actually wireless / WiFi at tbe destination, as opposed to requiring an Ethernet cable at both ends?

  @Goatboy 

You need to decide what is your objective.

1. If you want to extend Deco mesh using powerline adapters, you will need Deco compatible (supporting Deco Ethernet backhaul) powerline adapters set. It is recommended to get TP-Link powerline adapters brand, and they shouldn't have their own WiFi. Deco mesh provides WiFi.

You will attach Deco unit to powerline adapter at external area. This Deco unit will become part of Deco mesh, you will see it in Deco app, can see and manage devices connected to it.

or

2. You just want to have WiFi coverage in external area, having devices there connect to Deco mesh brings no benefit.

In that case, you can get set of powerline adapters with one having its WiFi, and that set does not need to be from TP-Link. In external area there will be WiFi, but it will be its own WiFi, even if you set it with SSID/password of Deco mesh. Device that is connected to that SSID/password will drop WiFi connection when it needs to reconnect to Deco mesh.

In case distance to external area is so far that Deco WiFi signal won't reach it even half way, device will be dropping WiFi connection when it is in dead zone in the middle anyway. In that case, this option to go with just pair of powerline adapters such as TL-WPA7617 KIT could make sense, and once again - no requirement for powerline adapters to be from TP-Link.

There is no third option where WiFi capable set of powerline adapters will be compatible with Deco mesh and provide seamless uninterrupted roaming between them and be managed from the Deco app.

  @Alexandre. Thanks again. 
I'm now confused. I assumed WPA7617 KIT would allow me to connect my external device to the same "Deco Mesh" network, wirelessly with the signal being sent via Powerline from Deco S4 to WPA7617. 
Currently Deco S4 is out of range of external device. I want to use Powerline to connect external device to the same network. 
 

Alternatively, I use your initial suggestion of PA7027P to do the same thing, except the connection to the external device at destination is via Ethernet and not wireless like WPA7617. 
 

WPA7617 description suggests I can use the same SSID and password as existing network ie Deco Mesh network.