@gjmartin 

Only two bands will be available for clients.  2nd 5GHz band is reserved for the backhaul only. Also, it will be active even when Satellite Deco is connected via Ethernet. That makes sense, because if Ethernet connection fails, Satellite Deco will be able to instantly and seamlessly switch to WiFi backhaul.

  @Alexandre, thanks for the reply, very informative.

This changes things for me then. For customers looking at using Ethernet Backhaul there is very little benefit for paying the considerable extra to get Tri-Band vs. Dual Band.

When looking at the band differences for the X68;

5 GHz: 1802 Mbps (802.11ax)
5 GHz: 1201 Mbps (802.11ax)
2.4 GHz: 574 Mbps (802.11ax)

I'm guessing the 1802 Mbps band is the exclusive backhaul band, so the only bandwidth available to clients would be 1201 Mbps + 574 Mbps. Whereas when looking at a dual band product (X60 as an example) that offers 2402 Mbps + 574 Mbps, so in a simplistic view and and looking at numbers on paper the dual band products would seem provide better available bandwidth to wireless clients when used in this way.

I would have thought that when the Deco units recognise an Ethernet backhaul or even if they are just running standalone, they would offer the full bandwidth to clients, and if they need to fallback to Wi-Fi backhaul they could prioritise the Deco traffic over other clients.

Maybe my view of Tri-Band has been wrong all along! Any idea if this is common across all Tri-band offerings with other vendors, is Tri-band a marketing term, which different vendors implement in their own ways.

Thanks @Alexandre. 

I'll definitely look at other options now, I had my mind set on Tri-Band, thinking that it would offer the most benefit. If I had to run all units via Wi-Fi then it would definitely be the best option, but using Ethernet backhaul it would make sense to look at Dual-Band offerings.

In researching Tri-Bands, it appears questionable over which bands 5GHz1 and 5GHz2 will use, with some stating that 5GHz1 will only utilise Band A of the spectrum, whereas 5GHz2 allows use of Band B. If this is true then the TP-Link Tri-Band offering means that Wi-Fi clients will never be able to benefit from the Band B frequencies, as this is only used for the Wi-Fi Backhaul.

With Dual-Band, the assumption is that the single 5GHz radio can utilise Band A or B, and will be available to all Wi-Fi clients.

Just to add for anybody else that is interested. Been doing some extra reading this afternoon.

Wi-Fi 5 & 6, Tri-band mesh is treated differently by the different vendors, most of them use a dedicated 5 GHz channel for the Wi-Fi backhaul, whether it is used or not (Ethernet backhaul), but there are others that offers a 'Dynamic' Tri-Band, and this should offer full bandwidth to Wi-Fi clients that can make use of it when used in a Ethernet backhaul configuration.