I lived in a 121 meter square single-floor flat with 3 bedrooms segregated mostly with concrete walls of around 1 feet thick. I have a 1gbps internet plan and household of 4 people with combined of around 10 devices connected during peak period, may expand beyond that occasionally. Planning to upgrade from WiFi 5 to 6, currently using ISP provided traditional AC5400 dual-band router with 4x internal antenna, with download/upload speed of around 350-400mbps without direct line of sight in my master room, around 250-300mbps (or 250-350mbps when lucky) without direct line of sight in 1st common room located beside master room, around 200-250mbps (or 250-300mbps when lucky) in the 2nd common room (this room is the furthest away from living room), and around 400-600mbps (or 400-800mbps when lucky) with direct line of sight in the living room. Device used to test is iPhone 13 Pro.

I'm currently looking at either the 3 pack version of X20 or X50 or X60 however I'm not sure which to go for.

I'm planning to have the main node in the living room since my modem is located there, with the second node connected via ethernet and placed in the master room, and the third node connected wirelessly in the 2nd common room as this room doesn't have any ethernet port. Other areas like the Kitchen and common toilet currently has stable connections since it's beside the living room while the master room's toilet located further away from the living room has weak connectivity including 2.4 GHz ones which would disconnect frequently so I would used 4G mobile all of the time, and 2nd common room doesn't really has the same performance compared to the other 2 rooms.