If you buy a VPN to protect your traffic from being tracked by Wi-Fi nodes while traveling, or to safely move your traffic back to the US, anonymous payment methods are unlikely to be very important to you. If you buy a VPN to avoid political persecution or want to remain as anonymous as possible, you will be significantly more interested in services that allow you to pay through anonymous sources, such as cryptocurrency or gift cards. Some VPN providers have systems where they will accept gift cards from major retailers (which are completely unrelated to their business), such as Wal-Mart or Target, in exchange for a VPN loan. You can buy a gift card at any number of major stores using cash, redeem it with a VPN credit, and avoid using your personal credit card or checking information.
