https://thatoneprivacysite.net/vpn-comparison-chart/
for example, i can see the ProtonVPN is hosted in Switzerland, and that Switzerland cooperates with Five-Eyes countries (according to Privacy International) by sharing intelligence information regarding citizens of Five-Eyes countries (including the US). this is a relatively mild concern, compared to VPNs hosted in one of the Fourteen-Eyes countries.
i can also see they use AES-256 for all data encryption. good. however, their terms of service and marketing material contain conflicting language regarding what information is logged, and details are not provided about how long logs are kept and whether these logs are personally identifiable. (running a truly "no logs" VPN service isn't really possible.)
at the network level, they appear to follow open standards and everything is implemented in a predictable manner. bandwidth looks good, but speeds and pricing are sub-par.
i've used ProtonVPN. i appreciate that they expose the details necessary to configure VPN using the built-in OS-level or router-level configuration screens, rather than requiring that you use their custom app. ultimately, the low speed (compared to similarly-priced VPN services) is what turned me away. it is neither the most privacy-conscious, nor most capable, nor highest value solution in the VPN market and i'm surprised to see this offering come through Mozilla. it's a weird endorsement.