@David-TP
Thanks David, that's helpful.
I have tried the older versions of Powerline before, and it was intermittent quality I think a) the wiring in the house is older and b) there are several ring main circuits.
Certainly the MAIN Deco would be on a different fuse box than where the first of the required Deco units would go. (It's upstairs with a floor and couple of walls between).
I've enclosed a screenshot from the app.
Basically the 'Lobby' is where the Fibre Router is (1Gb up and down), I have the 3 M4s coming off that, via a switch, and all cabled in.
If I went for a Powerline solution as the main Deco, I'd be nervous about it interfering in the backhaul traffic with the Cat6 satellite decos, which all seems to work perfectly now.
That said, I'm also concerned about the impact of wifi backhaul if I don't use Powerline upstairs, (and in the possible other weak zone if I bought 2 units).
Prior to the ethernet connections, one of the M4's was wireless, and performance was definitely significantly reduced.
Would the wifi backhaul be better managed by a new Unit in the (wireless) upstairs?
Or would it be OK to have a new Unit in the main position downstairs, connected by Cat 6 to the router, and put the M4 upstairs on wifi, with maybe 6-10 devices at a time?
Or even 2 newer units, one as main, and one upstairs wifi?
And which of the newer units do you think would be the best option to handle additional wifi traffic?
Overall I've got about 10-15 devices that are usually on, AV, Hifi, TV etc, and up to 10-15 extra when we have a full house.
The other alternative is replacing the cable, but that means getting up on the roof and buying about 75m of Cat6, and I'm also trying to keep infrastructure costs down as we may be moving on in 12-18 months, and a Deco unit can move with us.
Thanks again to anyone who can help