Double NAT from my understanding is where basically two routers are fighting over IP allocation. Hence leaving the Sky router to handle IP address alocation, and an AP of some sort simply to handle wifi, and ideally monitor/store/show device usage and apply rules (eg: bedtime).
I don't want to run a controller (eg: PC)? From my understanding the TP-Link Deco P9 will keep a history of usage etc and allow you to view it view a phone app.
Will the UniFi allow this, or as suggested do you need to run a capture server or like to achieve that?
NAT is where the router takes incoming traffic from a public IP address (the one your ISP presents to the world) and turns it into a private IP address range eg. 192.168.1.x and when you want to send data out again sends translates it back to your plublic address range.
With double NAT you might go from your public IP address to 192.168.0.x to 192.168.1.x and it’s just an extra step in the process. It’s not really a problem for most things.
With UniFi the controller IS the capture server. If you don’t want to run a capture server then UniFi isn’t for you.
I’m not aware of the TP-link unit you’re mentioning but if it better meets your needs then that’s great.
I use two systems for folks who want to analyse their traffic - UniFi and Untangle UTM. Both are what you would term capture servers.
If the TP-link unit does what they do, it must run a capture server on the access point, you’re just not aware of it. It takes a fair bit of processing power to keep up with everything that’s going on on a network, so the TP-link unit must be fairly oomphey to do what you’re suggesting.