@Imoq 

MESH option only works for devices that understand it. Disabling it will stop Deco mesh from telling device to switch to a different mesh node. 

The problem is, devices such as security cameras, TV and so on, they might not care. They look for an Access Point with SSID they are given, and connect to first one they can find. Perhaps, their software developers reuse WiFi code from old good times when everyone had just one router broadcasting SSID: if you see it, that's the only one to connect to. 

Nowadays mobile device must enumerate all AP with same SSID and select one with strongest signal, which is code rewrite these companies might not be interested in investing to. It is not their area of expertise.

General recommendations for improving mesh network.

1. Separate WiFi bands

If you can, separate 5GHz and 2.4GHz. Run Main Network on 5GHz only, Guest Network on 2.4GHz only. Use Main Network for bandwidth hungry devices and devices that support 5GHz but don't connect to closest Deco node. Use Guest network for everything else.

As 5GHz signal travels shorter distances, there is higher chance the Appliances sitting in the Living Room just won't see Third Deco on 5GHz and will have to connect to Kitchen or Main Deco.

2. Run Deco mesh in AP mode

If you run Deco mesh in router mode but don't use its features, switch mesh to AP mode. That might improve network responsiveness.

3. Wire all you can

Wired connection is always better than WiFi. Additionally, that will offload WiFi network.

4. Find spot for Third Deco with poor WiFi signal to Main Deco

It is not possible yet to tell Satellite Deco which Deco to connect to. Yet, if you can move Third Deco to a different spot, you might find one where signal from Main Deco is too weak and Third Deco will be forced to connect to Kitchen Deco. 

Install WiFi analyzer on smartphone, and walk with it to places where you can move Third Deco. See signal quality from Main Deco in all these places on smartphone, the worst is where your Third Deco should be relocated.

@Alexandre. 

Thank you very much for your insight. I do want to comment in a few of the points.

The cameras I'm using are Google Nest. Fairly new technology from one of the IT giants. If they have "old reusable code from good ol' times" it would be a shame on Google side as there is no logic on that. It's a multi billionaire company in any case. However, the cameras don't really give me too much issue so I guess disabling MESH for them is alright, I was just trying to understand if this is what we are supposed to do, disable MESH for "static" devices. If that's the case, then maybe Deco could have some kind of advise on that matter.

About separating Wifi bands. Really, I don't want to sound rude, but... what would be the point of having this great and "easy" technology if I would need to go and manually choose and decide if my device can see 2.4 or 5 GHz? I want my life simple, I just want to create a network and devices to connect to it and "just work". This is one of my main points why I switched to a MESH system, I just wanted coverage everywhere I put a satellite nearby without having to be meddling with network separations or anything else.

Wiring is also not an option because of exactly what I described above. If the house doesn't have any wires already in place there is no way I will start putting wires and holes everywhere. Again, this is the reason why I would buy a good, stable, modern MESH system so I don't have to do these kind of things.

Finally, it's a shame there is no way to tell a Deco to associate with the obviously closer one and instead having to try to trick it in order to connect to the one on the Kitchen. I did that and whenever the main one comes back, the third Deco would immediately connect to it, showing a weak signal because it has to go through 3 walls while it has the Kitchen one with just 1 window and a 6-8 meters garden between them. 

Anyway, I know you don't control any of it and I do appreciate your input and your willingness to help. I don't mind having to toss more Decos around the house if that solved the problem but I suspect it wouldn't, seeing how since now basically: 1) the devices tend to connect to the fartest away unit and 2) the Decos itself tend to do the same thing. For me this indicates a flaw in the design / technology although not sure if this can be improved or even fixed.

Thanks!

@Imoq 

I might have got sweet spot with Deco mesh, because my experience is positive. I have minor issue with Deco app, but that does not impact Deco mesh functionality.

I run mesh with set of three Decos: Main M9 in the middle of the first floor of the house, Satellite M9 on the second floor using wireless backhaul, wired Satellite M5 in the finished basement.

My in house WiFi coverage dramatically improved comparing with single Hitron Coda router I had from my ISP. Improved so much I disabled 2.4GHz on my Main network, to have devices get maximum Internet speed and roam better. My Android 9 smartphone used to fallback to 2.4GHz all the time for no good reason, until I disabled that band. 

I had to keep 2.4GHz on Guest network, because I have older ecobee thermostat and two other IoT devices that only work with 2.4GHz.

Occasionally a stubborn Microsoft Surface Pro tablet does not want to roam to the nearest Deco node, but it shows good signal from more remote node it is connected to, and its performance is not degraded. Its owner streams a lot on that tablet, if there were issues I would have heard about them, loud and clear.

Most of my house equipment is wired from old good times when WiFi was still a novelty, now with "WiFi everything" I only keep file, backup, print servers, 4K TV and three desktops all wired.

I spent a lot trying to get smooth video viewing on my main 4K TV that was not wired: WiFi extender, powerline adapters, etc. - nothing worked well. Eventually, I got fed up, took the drill and drilled enough holes in walls and ceilings to put Ethernet cable through to my 4K TV. Problem solved. Should have done that before spending hundreds on networking gear. Sometimes brute force is better than "smart" solutions. 

Disabling 2.4GHz improves mesh performance, and that will be true for any mesh system you are going to choose - that's just how this technology works. 

I am going to stay with Deco. It works for me. You don't have to. Good news it is not the only mesh system on the market. 

@Alexandre. 

Thanks once again for your input. It's great that you found a way for this to work for you. I'm staying with Deco for now until I truly find a better solution because I won't move away just "for the sake of it", I was just expresing my concerns and wishes for some things to improve, and asking a question about the use of the "MESH" switch.

Here is, hoping for the day a product gets released that can just work as advertised without having to be playing with different parameters (when possible, currently Deco doesn't even allow you to choose where to connect to, for example) and without having so many connectivity issues. Having a third satellite that can barely reach the first one and it being so obsessed to connect to it simply doesn't make any sense, no matter how much you want to defend this behaviour.

Cheers.