[Nextgrid]

I disagree. There are times when either no open-source solution is available, or the open-source solution is unmaintained, or not popular (thus not under much scrutiny) and you don't have the resources (time and skill) to audit it yourself.

As long as the incentives of the developer of the security scheme and the end-user are aligned (so no backdoors), I would trust a widespread, proprietary solution which appears to stand up to significant attacks (the solution being widespread means there are lots of efforts underway to crack it) more than an open-source implementation that nobody uses.