[butz]

"Small payment" is an understatement :)

"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."

[bardan]

Can confirm that after donating > 7€ I am still able to unlock pro features on new devices 8 years later

[bornfreddy]

And it is also opensource, so you can install it by yourself. But it is worth it (for me) to pay something to support the developer.