It's very easy to sign up, but you should be aware of the issues to cancel (see below)

The tool works exactly how it should and is easy to administer.

The fact that I do not have to manually take care of follow ups + number of times a person opens your email is a strong indicator of their interest. This was a new feature that I saw, which really helped me in better understanding the number of times etc. that I should follow up with a person.