I've been struggling with the M9+ since its purchase a few weeks ago.  Managed to set up the two nodes as routers, and am getting good coverage.

Have had many questions, some of which TPLink customer services tried to help me with.

Found and downloaded the manual, but it's of little help.

After much effort, I managed to get a Chromecast recognized by the main network, by trial, error, blunder and luck.

Problems continue.

Current problem:  Managing a Guest Network.

I set up a Guest Network, and it seems to be recognized in "Wi-Fi Settings" but not on "Select a Network":  why?

It's not apparent how to manage the Guest Network.

For instance, a guest's laptop is recognized and functioning on the home network, although it is intended to be on the guest network.  There's a second Chromecast for the use of the guest, but it is not recognized at all and is useless at this point..

There's no help in the manual (that I could find) on managing the Guest Network.

The acute problem (for the past wee is how to move a device (the guest's laptop) to the Guest Network?  And then how to add a device (the 2nd Chromecast) to the Guest Network?

So far this is no fun!