@TP-Link it's been more than a year I am waiting for a firmware update for M4 model. 

It's pain in the back to reboot decos everytime to get temporary boost. 

If M5 has it, M4 should also has it. 

Add me to the long, growing list of users whose 3rd Deco always selects the signal source of the main Deco, and not the Deco next in line or closets Deco.

Any solutions please!!!

These units really do not work as advertised... There is nothing mesh about a unit on the third floor connecting poorly to the unit two floors below when there is a unit on the middle floor... Wish I'd seen this forum and lack of support from tplink before buying.

Add me to the long, growing list of users whose 3rd Deco always selects the signal source of the main Deco, and not the Deco next in line or closets Deco.

Any solutions please!!!

Sharing one workaround that i found.  My setup:  3 units of x20.  One of the unit is connected to a regular router. so the decos are working on  Access Point Mode, I suspect this workaround will only work in this  setup. 

taking  the diagram from @mavericktan  

The "Main" deco (first floor on the right)  is connected via cable to the main router (non-deco). 

Set up "Room" deco and and "Hallway" deco as usual. 

Afterwards, in the deco app, set the "Room" deco as the main deco.

It's counter-intuitive, but this will force the "Room" deco to be the signal source of "Hallway" and "Main" 

Although the "Main" deco is actually still the real signal source for internet,but at least now the "hallway" deco is using the "Room" deco as signal source, and internet access and everything else still work as intended. 

See this on how to set the "Room" deco as the main deco.

https://www.tp-link.com/us/support/faq/2400/ 

  @getliu 

This is the best workaround. Tried and tested even on Router Mode.