The best vpn app for android that I have tried , so I had the opportunity to try the Surfshark vpn , protonvpn and lastly the mullvad vpn , and the winner for my opinion is mullvad.
1-It doesn’t drain you lot of battery from your device.
2-Gives you quite acceptable speeds .
3-Gives you the warranty of mullvad quality software.
I downloaded from google play, Open Source VPN. It’s open source on github and has servers in almost every country for free.
I can admit that Mullvad VPN is very flexible on how you can use your VPN , I mean they give you the option of downloading their VPN app , that in my opinion is very friendly with your device, using the Open VPN configuration files, that in my opinion is a good option , but not the more fast for having a decent internet browsing , or finally the Wireguard configuration file that might result for some people a little bit trickier to configure.