The thing with those pay as you go VPN services is that you are being routed thru their servers and they can log, track, control all of your internet activities..
You can choose the country you want your VPN ip address to be coming from, so say you are connected to an open wifi in the US, but if you choose a VPN connection to come out of say Canada, that's really the only thing that's happening with that VPN connection.
No additional "security" from that same open wifi.
Your computer is still using an IP address to that open wifi connection it gave you to connect in the first place. The VPN connection you have is just changing the IP address that the web sites you are going to sees..
Anyway, I looked at the Nord VPN and tried it, but cancelled it a couple of days later, as I found out that it simply does not make an open wifi any more secure than just using the open wifi.
When you connect to a new network, your computer should prompt you to select the type of network you are connecting to. At that point, you should select the "public network" option, as that will set your computers firewall to be not let your computer to be visible on the open network.. Nothing is ever 'secure' as such, but I still would not conduct my banking or other password entered web sites from an open wifi, even using a so called "VPN" connection..
Good luck!
Mitch