So, everyone, I went with three MR2200ac by Synology.

Thing, is, we'll spend some time in a house my family has in the mountains. My wife and I will need to work remotely from there and I had to get some wireless devices before our departure, end of July. So, I kept learning about mesh and I felt I knew enough to
- Get three mesh devices for my home here in the city, and
- Move all "old" Wifi equipment to the other house.

Usually that's when you make some silly mistake. Instead.

I ordered 3x MR2200ac yesterday, and today my mesh network is up and running - amazing Amazon (delivered in less than 24H!), and amazing Synology. Quite impressive stuff.

After setting up the main AP (controller, let's say), you have to add all other APs via wireless, THEN you can plug an ethernet port and the system will move to wired backhaul.

Signal reach is obviously much better than before in previously weak spots.
What is impressive, other than the great RouterOS, is that I tried several times to power down an AP where my laptop was connected, streaming from youtube, and it did not even notice. Roaming is, after few hours of testing (so, very little time) just flawless. I hope that keeps being the case.

Overall, I spent € 450.