Always be careful with free services like this. How exactly are you making money? If your response is along the lines of "this is our version of advertising", then its bullshit and you're selling data. Any free VPN service is selling data, it's the only way to run a sustainable business. Paid VPN services these days are cheap and you can pretty easily get subscriptions via Bitcoin or even gift cards. PIA is a cheap and reputable service, vs something like this.

Again, I'm not trying to trash this service or anything: I actually think it's very nice to offer something like this. But it's important to be skeptical, especially when involving VPNs, as the industry is incredibly shady. I even have issues trusting the established companies, even less the ones that pop up out of nowhere.