I commented about LessPass, and I think it applies here too. In summary, you still need to run MasterPass to retrieve their passwords, not here.

Security-wise, my construction might be slightly less secure, but you can recover the same level of security with a slightly longer passphrase (and, unless I misread their code, they also use a deterministic salt in scrypt, which is a debatable choice).

As I said about LessPass, it would be great to hear from the author(s) what they think.