@David-TP Thanks for the welcome and the reply.

You said... "I am quite curious why you want to prevent a certain device from connecting to a specific Mesh unit. Is it due to the lower wireless speed on the AC1200 or something else?"

My set up, forced by circumstances and not easy / cheaply changed, is that the 3 x X20 units are physically connected to the house's network, whereas the AC 1200 can't be (it has to be where it is and there's no LAN port nearby) and so is wirelessly connected to the "Main" (primary) X20.

Annoyingly, the location of the AC 1200 is bang in the middle of the downstairs area meaning that it's often the unit which portable devices and a work laptop connect to whilst at the same time I've noticed that it tends to deliver internet speeds a bit lower than the X20s.

Hence I was hoping to have the AC 1200 only having nominated devices connecting to it, meaning all other devices will connect to any of the X20s only.

It is what it is, thanks for your interest.

Cheers, Daamon.