Using someone else's WiFi isn't a security advantage, it's the opposite. You're bumming off of someone's network and not even paying them - so who knows what their motivations might be. Who knows if the network that the SSID claims to be is actually that network.
Is Starbucks Free WiFi actually run by Starbucks or is it a malicious router placed in the same vicinity? I don't actually know until I connect.
I would suggest the alternative of using a pay-as-you-go plan on a SIM card, something that doesn't cost a lot with low usage. If you want to be more disconnected you can simply turn on airplane mode. In almost any country in the world you can pay less than $10/month to maintain a phone line and SIM card.