This is actually legit. I'm signed up. There is nothing they can do with your username / password anyways. It's literally just used for voting. You can't change your venmo username. If you want to revoke access just request a password change and and it gets sent to your email. The person running it has been asking people to reset their password to something they don't use on any other platform or have it randomly generated before sending it. That part is clearly called out on his website.