This is really cool, and its an interesting way to try to monetize what would otherwise be a relatively small service.

The big issues here are trust and security. Before using a third-party login, especially if it isn't one of the big ones, I would need to understand more of how it is handling the data. A breach in your service translates directly to a breach in mine, and the intro page does not describe many of the details.

Does using your service offer the end users any benefit compared to a third party login or built-in login service? As it stands, it seems like they will be giving their email address to yet another company, which may erode their trust in my own service.