Hi -  I just installed a Deco M9 Plus.  Easy install.  Everything worked fine after the firmware update (before that Amazon Prime Video channel was not working).

I have 300 mbs fiber service from AT&T.  With a PC plugged directly into the AT&T Arris BGW210-700 modem/router, I get 365 mbs.  Plugged into the Deco M9 which is plugged into the AT&T device, I get 365 mbs.  So AT&T is delivering and both devices are being well fed.

Using the same PC with wireless only and no VPN with the Arris' WiFi switched off, I get 20 - 30 mbs.  That is less than I can get directly from the Arris via wireless.

Using various devices throughout the house including a second Deco on the second floor, I ocassionally can get 80 mbs but also can pull 6 mbs.  About the same as with the Arris alone.

T-Link tech support told me that in addtion to the set up I did following their phone app, I either have to get AT&T to put the Arris in Bridge Mode or set it up as an Access Point.

Using the M9 as an Access point negates the free security software and seems to defeat the purpose.  AT&T uses dynamic address so not sure about the Bridge Mode.

My first thought is to box it up and return it and hope the next brand provides simple set up as promised.  But I thought I would see if anyone has experience with this issue.

Thx much in advance.