Hello, I'm after some advice please: I've seen a lot of good things about the Deco range and and know that TP-link is a good brand.  I want to invest in deco for my home and get a good setup as wifi is currently terrible.

After starting to look through the range I'm getting confused by all the variants available, so would appreciate some advice.

Here's my thoughts / requirements:

• I feel unsure about how the mesh links to each other.  I understand how powerline works, but if I don't use powerline, do the units have to be physically linked via ethernet cable?  Do they link wirelessly, and if so what is the performance difference between wireless and ethernet?
• I like the deco P9 style and think 2-3 of them would cover my home effectively.  However one of the locations would be almost impossible to run an ethernet cable to.
• I'm with virgin but in the evenings the speed often slows to a crawl (0.5Mbps!).  I'd like to include a SIM 4G router in my setup that I can bridge to the network to provide a 4G failover connection.

What products do I need to achieve this effectively?