As far as I can tell, yes. I signed up for the free tier before paying for the service, and the worst I ever got was a banner here or there advertising their paid service. Proton encrypts all your data with your password, so they literally can’t access it even if they wanted to. The only info they have on you are things like when you logged in and your IP address (and I believe they’ve turned that info over to law enforcement when required, like any legitimate company would have to do), but their servers are in Switzerland where there are better privacy laws.