I have heard good things about this one. But i think this one of those no root firewalls that uses the vpn, so I figure this means I can't use a VPN at the same time.
An alternative android root only option is afwall+ which allows blocking on lte, WiFi, lan, and VPN separately, and script access to iptables. Not sure how actively developed it is, but it seems to work ok.
*edit: Seems to still be active, open source, and available on fdroid too.
Netguard is fantastic, although it takes a while to get a safe setup working. I'm blocking traffic by default and get to see all the blocked connection attempts - the extent to which apps transmit data to various parties is depressing. Netguard should be a standard OS feature.
I didn't want to pay without testing the features first, so I have rebuilt the app (it is opensource) with Pro enabled, so I guess that's an option if you want to avoid payment. Updates are a problem then though. Once I tested it I gladly paid (more than requested) to support the development. I never got around to reinstalling it though, so I'm still on an older version.
NetGuard is simply awesome. The piece of mind when I know which servers the apps are contacting, and being able to block their access to the net by default, is just great. The rules could be made a bit more easily adjustable (it would be nice if I could block `*.firebaseinstallations.googleapis.com` everywhere, even if other traffic is allowed for the app), but I'm just nitpicking now. Highly recommend it.
"You can get all current and future NetGuard pro features (including updates) without Google Play services for the GitHub or F-Droid version by a one time donation of € 0.10 or more. If you donate 7 euros or more, you can activate the pro features on all Android devices you personally own, else you can activate the pro features one time only."
An alternative android root only option is afwall+ which allows blocking on lte, WiFi, lan, and VPN separately, and script access to iptables. Not sure how actively developed it is, but it seems to work ok.
*edit: Seems to still be active, open source, and available on fdroid too.
https://github.com/ukanth/afwall