The only way to ensure that data isn't leaked prior to encryption is to only ever think and never let it leave your thoughts. These password managers are secure, your larger risk is the safety of your host device as that makes the easiest target.
I doubt you'd be an interesting target mind, most malware doesnt hurt you directly, it turns your device into a weapon against someone worth attacking.
What you're talking about is illegal for the company to do. They're not some "random bloke" they're a company just like any other. In many ways i'd have more trust in a single bloke who's name i can find than the faceless generally pretty terrible banks of the world lol.