Open source client doesn't really get you much, since you would need to audit the entire source code, then build it yourself, which you probably won't do. If you aren't doing that, you're implicitly trusting others to have audited the source code, and to provide builds that actually correspond to the source code. Now there are reasons to trust the open source community like this (lots of eyeballs, and people who care about security and privacy can inspect the source code and third party builds), but there is also one advantage to commercial software (including closed source) over open source: you're more likely to have someone to sue if they lie or mess up.