I just updated to the latest firmware which includes the OneMesh feature. When I updated, the TP-Link Cloud functionality wasn't working properly (it would keep giving connection errors on the firmware check and cloud login), the Admin Account option was hidden and worst of all, I wasn't able to do a factory reset properly. First I tried via the web GUI, it was stuck on 0%, when using the button at the bottom of the extender all the lights would come up but nothing happens. Switching it off and on at the mains got the extender to reboot but it wasn't properly reset.

I then discovered changing the IP mode back to Dynamic (and using DHCP Address Reservation on my Archer C6 to give it a static IP) and the cloud features started working again! Factory reset also works in dynamic IP mode.

So clearly there is a bug when on static IP mode and while there is a workaround if your router supports DHCP reservation, it should be fixed as soon as possible.

BTW, do multiple reboots and resets of the extender shorten its lifespan? I've done it about 10 to 15 times to figure out what's going on.