hey man did you at least consult an attorney before you "accepted their kind out of court settlement"?
Shark attorneys have a way with language to intimidate the shit out of you. IMO for them to prove you were infringing would be quite a burden, especially given the fact that you aren't charging for software. It's like windows media player suing winamp. Makes no sense. Keyword grouping is not an uber-secret formula or anything like that.
just my 2c