Do not tell your members about it though otherwise he/she may view the post before creating a new account and simply know to delete cookies before attempting the next registration.
Using this mod you should be alerted when they signup a new account .
Does it have false-positives? Yes but rarely.
When would this not work well? In situations like dorm rooms and such where a universal computer is used and more than one person know about and use your site from said pc.
This will not ban the member, it will alert you then you can review and take the action you deem is required.
This is a great plug in but had issues for me recently with Vb4.2.2. This could have been something minor though, I just do not remember the exact issue other than nobody was able to log in.