Recommended (free) VPN Service for Android with .apk download outside Play Store for low data use?

With download outside the Play Store but from a trusted source?

 

You can use any VPN that supports OpenVPN and then download the opensource client from here: https://code.google.com/p/ics-openvpn/ There are other clients too. Check FDroid as well.

 

OpenVPN for Android is very easy to use. Easier than the Windows version to set up.

For low data use, there are many free VPN options that support OpenVPN.