I don't use VPN. I downloaded the app you mentioned but I don't see anything major.Just out of curiosity, is there a lot of data being sent to and from your device? And do you use VPN services?
Its hard to track the amount of WiFi data being sent on the iPhone without an app, but there are apps such as "usage device monitor" and many others than can give an idea. Would be interesting to see what's going on in the background on your device.
To be honest my use case hasn't changed for years now, it's been the same, the same apps all the time.