TP-Link Deco-M4 Whole Home Mesh WiFi System

i have sb s6782 ac (Arris surfboard) connected to xfinity high speed. Unit manufactured in 2014 and as of sort of recently I think, I can no longer log in to device at 192.168.xxxxx. But the device still works. But my 5ghz wifi speeds dropped to about 70-80 mbps and seemed intermittent. Youtube tv doing lots of buffering and chromecast devices constantly disappearing from network. 2.4 ghz speed also dropped (to about 25-30 mbps). I plugged ethernet cable to mac computer and got speeds of 220-230+mbps from the old Arris. So I figured if the device could still pull that speed from xfinity I would try to continue using it. Remember In order to see how well a new device works you need to know how good the signal is that you provide. So I suggest testing current modem/router or whatever set up you have via ethernet as place to start, as well as test the speeds of both bands of your current modem/router. So I Bought the 3 pack TP-Link Deco Whole Home Mesh WiFi System (manufacturer refurb). Set up was not difficult. I have an open loft townhouse. First device sits next to the Arris connected by ethernet cable. Second device in living room about 45ft away. 3rd device in loft about 25 feet from second device. My 5ghz speeds are now 200-250 mbps depending on time of day regardless of unit (you can see which is used). 2.4ghz speeds are 45-75 as well. If you are wondering why the 2.4 ghz speeds matter...i have 2 chromecast speakers and a chromecast audio that run on 2.4ghz, so my phone also has to use that network. Moreover, casting to all of my chromecast speakers has become stable. No device has ever disappeared from the cast view (i cast amazon HD music from phone every day several times per day). Additionally my google tv (the usit google tv sent to subscribers due to roku fiasco) works so much faster on this 5ghz connection. Important: The Deco S4 comes equipped with only wpa security and all of my computers were suddenly warning about the security level (or lack of security). So I was not thrilled. But there is a firmware update for the deco s4 (update is v1.5) and it has the option to switch to wpa2-psk (AES). But the user forums were full of complaints that the update caused their speeds to crash. Yikes, and there were many complaints. I waited for a few days and decided to to the firmware update and if my speeds crashed I would simply return to amazon. The update was easy to install, and my speeds did not crash, and it seems as though the addition of the "network optimization" feature (which i ran) helped get the speeds up. So all in all it is a massive success. One more important note (which is a negative item with a solution)...the deco does not display both network frequencies. So my devices with 5ghz will all grab 5ghz, which means my samsung note 8 could not get onto the 2.4ghz that is required for casting to the 2.4ghz chromecast devices. The solution is to set the guest network up and so now there are 2 networks. And each network can be set to either be 2.4&5ghz, or 2.4ghz only, or 5ghz only. So I made one network 2.4ghz, and one 5ghz. It works great. Eventually I'll replace the Arris with a modem only device.