@Shrops 

There is also M9 Plus, it is WiFi5 and supports connection preference.

There is not much benefit of getting X20s, especially if your Internet link speed is 500Mbps or under. If you have faster Internet, you may get faster speeds from devices connected to Main X20, but for the rest of Deco mesh speeds will be about the same they are now.

If excluding X20, my recommendation would be M9 Plus over M5 over S4.

If selecting solely by price, any from that list can do including X20, as long as their firmware supports connection preference you need.

  @Alexandre. 
 

Thank you for that comprehensive reply.

I have 500Mbps (my ISP can provide 1Gbps but I don't need it).

Do the X20s provide better range than the M5 maybe? If so, I may still consider those, as I can then provide better coverage into the garden.

TIA.

  @Shrops 

In general, WiFi6 is faster than WiFi5, but on shorter distance. Which means, for range one should compare WiFi5 signal from X20 vs. M5, or even 2.4GHz. WiFi 6 will not reach farther than WiFi5.

I have M5 and M9 Plus, M5 has less powerful antennas than M9 Plus. Can't tell much about X20, but it is the most budget model in Deco WiFi6 X-series, so make your conclusions.

If range is important, try either M9 Plus (more powerful than M5) or X55 (mid-range WiFi6 by price/performance, supports connection preference). I can't guarantee they can provide necessary coverage, but both should be better than M5 when it comes to range of WiFi5 signal.

  @Alexandre. 
 

Thanks again.

So, my choice is now M9 Plus or M5.

Connection preference is a must for me. I know that all versions of M5 now offer it.

According to the link I shared earlier, the M9 Plus versions that support it are v1, v1.2 and v2. I think there is also a hardware version 2.2 though, which isn't listed in the article detailing the models that support connection preference...

  @Shrops 

Check TP-Link UK Support link for M9 Plus hardware 2.2: https://www.tp-link.com/uk/support/download/deco-m9-plus/v2.20/#Firmware

It shows latest firmware 1.6.2 for hardware 2.2. Firmware 1.6.2 does support connection preference: Understand the Differences Among Deco Firmware Platforms

  @Alexandre. 
 

Thank you again.

I think I've decided on the M5s, given that a twin pack is £60 cheaper than the M9 Plus.

Next question. I've already mounted my main M4 on the wall next to my ONT. Is there any reason I shouldn't keep it as the main, despite adding M5s to the setup?

TIA.

  @Shrops 

You can keep M4 as Main Deco. If you were going with M9 Plus, it would have made sense to make M9 Plus Main Deco. M5 and M4 are very similar in performance, so there should not be necessary to change your Main Deco.

When you are adding M5 to Deco mesh, Deco app might suggest making M5 new Main Deco. Just dismiss that suggestion and M5 will be added as Satellite Deco.

  @Alexandre. 
 

Thank you!