I suspect the issue people have is that it is not possible for the average user to confirm that a block like that is working 100%. Seen as google control the OS they can just route their traffic around a block like that if they wish. Sending the data over 4g would mean you don't even see it on your network traffic logs.
There are a number of reviews suggesting it intermittently lets aupposedly blocked traffic through too, but the biggest issue maybe the way it works. As far as I can see, it acts as a VPN, but that means it won't work well with other VPNs, which is another way the traffic can leak.
Basically, installing an app like that doesn't degoogle your phone at all, it just makes you feel like you've stopped your data leaking.
Unfortunately there doesn't seem to be a way to link to a filtered set of reviews on the play store, but If you go to the store, find the app, go to the reviews and filter by 1 star you'll see them. Some of them just don't understand how the app works, as you say, but there are a number that are harder to ignore.
The thing ism if it is acting as a pseudo VPN, it could easily leak when the OS suspends it (for power saving, switching network modes or the like). Honestly, I haven't tested it, it doesn't do what I need (I'm on another VPN a lot of the time), and I wouldn't trust it very far myself, but if it does what you need, that's what matters.
I personally observe with my own eyes many many times where Android turns off Adguard's VPN for a split second when doing various Google things like receiving messages in Google Messages.
I haven't been able to pinpoint it but my observation is that the disconnect/reconnect happens when a connection is trying to be made (ex. RCS message incoming), and I suspect Android is dropping the VPN to make its own connection. Sounds paranoid, but I've been carefully watching it happen for a long while.
I’m not sure if you’re dense or just pretending. You talk about a piece of software and I refer to their faq. I’m sure you have researched your claims and read up on this software….