It is open source. https://github.com/subhra74/xdm-integration-module

Windscribe and Proton are also free but they're much faster. I recommend trying them first.

Paiphon and Windscribe are good. The former gives you unlimited data, while the latter only provides 10 GB per month but has a court tested no logs policy.

I use XDM. It's open source, has no ads or other shit, and it will download almost any DRM-free video on a web page.