This may not be the right place to ask but I've never looked at routers before. If you have a service from Sky for example, do these replace the Sky modem or do you have to run your line in to the sky modem and then in to one of these for the home network? When it comes to MESH I assume these connect to each other at the highest possible connect rate and then output the multiple bandwidths for any devices that require it (Wifi 6/AC/etc)...

This device would replaced your Cable Modem and router since it is a all in one device. Mesh is what you are thinking. The router most likely gives out a wireless signal and the 2nd device connects back to the router to give out a wireless signal as well. The device that you want to connect to wifi will see 1 SSID and no matter where you are at as long as you can see the SSID you will be able to connect to the internet. Mesh is nice since it allows your device to move from one Access Point to another without having to change SSID's. The only downside to a device like this is that if one thing goes bad, you have to replace everything at once.