@SnaffyNoo 

Decided I'd go with the M4 models for a few reasons.

Any tests I've managed to find seem to place them pretty much neck and neck when it comes to performance.

The shape of the M4 with the Ethernet cable placement holes are just more suitable and practical for the locations I wish to put them.

Will admit I don't really understand the shape difference, obviously I know nothing about Antenna design! but if I did not have any clue

and you asked me which is the better I'd have said the taller one for more antenna height/space? but hey...... LOL

Oh and there is a good price on at the moment, hence why I've gone for two double packs.

However was rather annoyed that I paid online, drove to the store and they only had 1 pack in stock.... Grrrrrr

Late today or early tomorrow they should have the other set.

Few issues setting up, WiFi from phone to 1st unit, then had to turn mobiel data off, but after a few hiccups, got it set up.

All was going fine, till I hooked up to my Dlink Switch (I recall a story about issues with some Dlink switches)

If I'm honest, of I did not know of this story which I only read by chance, I'd have packed it all up for a refund as not working.

Thankfully I did remember, and again, by total sheer lucky fluke I had purchased a spare Gigabit switch a few years ago

(Amazon deal) that I'd never even unpacked.

Swore a lot, trying to find where the dam thing was.... that took about a hour of hunting, but eventually found it.

Plugged in, and all then worked fine.

Have run Backhaul to the second unit, and will run bachaul to the others when I get them.

Without backhaul I'd not touch this stuff with a barge pole as the performance is just destroyed without a wire into the back of them from the switch.

With all that said, so far with 2 units running, all seems very good, and very happy with my choise, and the price.

Just need to do a battery test of my Phone/Tablet as my previous Mesh (Tenda Nova) worked fine but will killing the phone/tablet batteries for some reason.

Fingers crossed the my new Deco's don't do that..... :)

@SnaffyNoo could you comment how this ended up? How are you chaining your different M4's?
I think i will try one of this config to expand ETH ports and use ETH Backhaul:
A) ISP Modem/Router (Bridge Mode) --> 1st Deco M4 --> 1st TL-SG105 (Switch) --> 2nd TL-SG105 (Switch) --> 2nd Deco M4 --> 3rd Deco M4

B) ISP Modem/Router (Bridge Mode) --> 1st Deco M4 --> 1st TL-SG105 (Switch) --> 2nd Deco M4 --> 2nd TL-SG105 (Switch) --> 3rd Deco M4

As you can see, i have 3 "stations", thats why i have 2 small switches.

Hope this helps someone! :)