They are offering a free tier of service, so if you were curious about potentially using a VPN they're probably a good place to try it out at right now. Presently there aren't any speed differences between the free servers and the paid servers, but most likely free users will start getting throttled once more people start using the service.
For those under a rock, ProtonMail was one of the first user-friendly services offering entirely encrypted email service. They have a very good threat model and are based in countries with good privacy laws, making them an excellent choice if you're concerned about government-sanctioned surveillance. If you're not concerned about that, then most likely any regular VPN is enough for you to avoid ISP tracking.
https://protonvpn.com/