With any of these third-party apps, I would always caution you about inputting information like your personal and for-real DVC login data (or any login data for another system). I'll note that using a Google or Facebook Connect login is somewhat different, as that uses a known protocol and there is no pop for the app to swipe that data.
The site and app claim not to store your DVC login, but you have to trust the totally anonymous maker of the app on that. Who also says the data shown could be wrong or completely made up! Now, make your own decision here, but that's not confidence-inspiring.