So you wouldnt trust a random wi-fi, but you would trust just any old malicious VPN you happened to find on underground forums. Thats bad advice.
This. VPN provider can read and modify and save all traffic.
The best way to stay safe when being connected to an open wifi is to connect to your own vpn server at home.
Simply get a raspberry pi if you don't want to have your PC running when your not at home, and install OpenVPN.
You will be able to route the whole traffic through your home-network.
When only rarely being in an open wifi, this seems to be overkill. But if you regularly use open wifi's it might be worth to get a raspberry pi to host a vpn server.