Hey,
Proton Pass is open source and has now passed an independent security audit (by Cure53). The Android and iOS apps source code can be found here, the browser extensions source code for Firefox and Chrome-based browsers (including Edge) can be found here.
Proton has also completed an independent security audit conducted by Cure53 for all Proton Pass applications and browser extensions, along with the Proton API. This was a “white box” audit, meaning the security researchers were given full access to the Proton Pass source code, along with full access to Proton Pass engineers.
More information can be found in the blog post over here. The audit report can also be found in the blog post.
Not sure if I qualify for that, but just logically, there’s only really a difference if you are not planning on storing your email password in your password manager anyway. If you do that, it doesn’t really matter that you have the same password for both, since if your password manager is compromised, your email is just as compromised.
But, and it’s a big “but”, that’s assuming you’re using a cloud-based password manager that only requires a single master password to get into. My point of reference here is 1Password, where that’s not enough - you also need a device with which you have logged in before, or you need your long, unmemorable Secret Key in addition to your password. You cannot log into 1Password on a new device with just your master password, the way that it appears to be possible with Proton.