This plugin requires you to register then the author sends you "promotional emails".
"Yesterday a friend asked me, why SEO SearchTerms Tagging 2 plugin must be registered now?
This is my answer: I want to be able to communicate with you, the
plugin users. Whether it is sharing information regarding WordPress
and SEO, or just giving you a more detailed explanation about the
plugin and how to optimize it.
Yes, sometimes I'll send you a promotional email..."