I have just bought the Zyxel mesh system after months of trying to pick a decent platform. So far its working just fine and does what it says on the tin.
Read some of the reviews and watch some of the YouTube clips.
I have it sitting behind a standard Openreach modem although you can use a normal router set to bridge mode the same way.
I discounted the Netgear Orbi after reading extensively about the constant firmware problems and also I have recently sent back a Netgear D7800 because of another issue regarding not being able to detect the DSL cable.....
If you have any specific questions that I can answer about it please feel free to ask.