How are they going to 'login'? If it's a link with a unique id associated with the email address, it's essentially a password that can't be changed. The fact

How are they going to 'login'? If it's a link with a unique id associated with the email address, it's essentially a password that can't be changed. The fact that a person will need to keep opening their email is really a deal breaker. Usage will drop off pretty quickly.