When I uninstalled the plugin it was still there and they wanted to charge $49 to advise how to remove it!!
We have extensively tested the plugin and we can guarantee that the link does not stay after the plugin is uninstalled. I would guess that you have some cashing extension that causes this problem with your particular websites. However, we cannot say for sure without testing it on your website.
We would like to thank you, however, for the feedback about the backlink to our website. We have added this token of appreciation since it is a standard practice amongst such extensions but we will consider making it optional for the next versions.