This add-on does exactly what it says it does - very happy with it. I was getting sick of YouTube flooding my recommendations with videos I have already seen, and the YT 'Not interested - Tell us why - I've already seen this video' seems to have little to no effect these days. Be aware that there is a 'threshhold' setting with this plugin which you may need to tweak for best results.

EDIT - guys, if you use this plug-in and like it, please support the creator with with at least a few stars.