OpenVPN Connect is the “official” app from the OpenVPN Inc. and is designed to be more user-friendly for VPN users with minimal technical experience. It is less feature-rich than openvpn for Android, which is designed towards more advanced OpenVPN users.
Openvpn for Android is a no-cost open-source client developed by Arne Schwarzbe, enables you to connect with any VPN service that is compatible with the OpenVPN protocol. It’s a great choice for devices that aren’t compatible with pre-configured “off the shelf” VPN apps that are available on the Google Play Store. The setup process is quite simple. You only need to import your VPN profile files (the config files have an extension of.ovpn) which you can find on your provider’s website or by contacting their live chat support team.
After you’ve imported a profile, simply tap on one of the servers listed and connect to that server. Once connected, your Internet traffic will be directed via a secure channel to the server specified in the application. The Status tab allows you to examine your connection’s information and the status. A kill switch is always enabled by default. It will also disable your Internet connections when the VPN tunnel is lost.
The application also offers per-app VPN and an on-demand feature that automatically starts an VPN connection when the app is being used and keeps it running even after your device goes to sleep or switches networks. However, this feature requires Android 7.0 or higher and could draw more power from your battery than normal.
http://openvpnandroid.com/nordvpn-vs-ipvanish-vs-expressvpn-vs-openvpn/