I based this plugin on my own experience of what I find useful when visiting and revisiting a blog and on different plugins addressing parts of the needs. However I appreciate your feedback in improving this plugin, so feel free to comment!
Are you able to deactivate sections of the logic? I don’t think “The first post a visitor came to on his previous visit” is relevant to my site, but the other search conditions are. Also, I probably would want to control the application of any more database intensive queries on my site. It doesn’t need to be any slower than it already is!
Yes you can choose which logic to use per widget. Regarding the effect of database intensive queries: I guess what that also depends on the speed of your web server and the number of visitors. Currently this is not cached by the script, although the MySQL server might do that.
Give it a try and let me know your experiences.