I've recently setup TP-Link Deco M5 with 3 units.  One is the primary/main unit and connected directly to my modem, and the other two are connected via Ethernet backhaul. 

So, in ASCII art diagram form:

<modem> ---- <deco M5 main> ----- <dumb gigabit switch> ----- <deco M5 #2>

                                                                                             \

                                                                                              \

                                                                                                -----<deco M5 #3>

I have another router/Wifi AP, the Turris Omnia, that I'd like to add as a fourth unit, i.e.

<modem> ---- <deco M5 main> ----- <dumb gigabit switch> ----- <deco M5 #2>

                                                                                             \

                                                                                              \

                                                                                                -----<deco M5 #3>

                                                                                                \

                                                                                                 \

                                                                                                   -----<turris omnia, deco mesh point #4> (proposed)

My question is this:  does the Deco M5 system support third-party mesh points?  If so, what protocols do I need to use in order to set my Turris Omnia up as a fourth wireless mesh point? 

Thanks in advance for any tips on this!