Does it stop data from leaving your device or just collect it all as a proxy and refuse to forward some of it. I'd much prefer to not have to hand all my traffic over to anyone offering a free app and just trust them not to use/abuse it.

How these apps "should" work (IDK how this one does) is use the VPN API to capture traffic then filter it locally. The traffic should then leave the device as regular internet traffic, no VPN tunnel.

This is how it works. Downside is that you can't also use a VPN alongside this. (Maybe that's changed haven't used it recently.)

Thanks for this. How do I trust their VPN is not just harvesting my data?

It's not a VPN service like the type you'd use for privacy. The VPN part all happens on your device so there's no data being sent to a third party for them to harvest to begin with.

Not sure if that is what you meant. If your concern is more generally about the app being malicious, I suppose you could audit the source code. But this is not something I have done or even am qualified to do, so I don't know.

Thanks.