The free service starts at only 500MB per month, but you can lift that by 250MB if you register with the service and by 500MB for each friend you get to sign up. Free users are limited to connecting to servers in only 16 countries.
Like ProtonVPN, the gives you an unlimited amount of free data per month. But its network download and upload speeds were awful (download speeds were 3 percent of the baseline speed), and it's not even a real VPN; it's just a browser-specific encrypted proxy service. (The OperaVPN mobile apps no longer work.)
To assess free VPN services, we gave them a thorough test drive from a suburban New York office and home. (We tested a 10th option, the experimental VPN Gate project, from a midtown Manhattan office, but that service's speeds were so poor we can't recommend it.)
2.2 Unauthorized Account Use. You agree to notify Purch immediately of any unauthorized use of your account or any other breach of security. We will not be liable for any loss, damages, liability, expenses or attorneys’ fees that you may incur as a result of someone else using your password or account, either with or without your knowledge, and regardless of whether you have or have not advised us of such unauthorized use. You will be liable for losses, damages, liability, expenses and attorneys’ fees incurred by Purch or a third party due to someone else using your account.
Speedify's drawbacks are that you can't connect manually (it's software-based), the cellular-data usage will cut into your carrier's monthly limit, and it's based in the U.S. and subject to search warrants. The free services is limited to one device, although you could just try to create new accounts for extra devices. But even free users can connect to any of the 1,000 or so VPN servers in 40-odd countries.
limits its free tier to only 1GB of data per month, and that's only if you register with a valid email address; anonymous users get 500MB. But this service is easy to use and reasonably fast, making it perfect for checking email while you're in an airport waiting for a flight.