I previously had a main router Deco M4 and the secondary was Deco E4. Although they worked fairly well, I wanted to receive better service because, for some reason, the network connection in my room wasn't very good, even though the router was in the next room.
 

So, I switched to two Deco M5 units. The service improved a bit, but the speed under the M4 was no longer achievable, and it has significantly decreased. Moreover, where the E4 used to provide coverage in the next room, the M5 provides even less. My room situation has worsened. Where I used to get link speeds of 30-50 Mbps, it now drops to 2-3 Mbps.

Now, I assume this issue with the link speed in my room is due to my phone (Samsung M21). However, I didn't like how the speed dropped from room to room.

So, I've temporarily switched back to my previous Deco M4 in my room. While this fixed the coverage issue in my room, I lost many features.
 

Now, I don't want to replace the M5 units, but was considering upgrading to X20. However, the cost for a three-pack of X20 is quite high. If I buy a two-pack of X20 and mesh it with the M5, removing the E4, will I still get all the software features? Currently, by keeping the M4 connected, I am missing many software features. I know I won't get WIFI 6, but will the network be seamless?
 

Or should I remove the M5 and go for three sets of X20? (I prefer not to do this.)

Thank you.