Good but outdated Rated 3 out of 5 stars
So many good scripts are combined into this add-on, specially the prewatch script... but the problem is that, most of these scripts are outdated so is the add-on itself.
Since Youtube updated its API multiple times in last year, that's why you'll get various glitches/errors if you use this add-on .i.e. The blank thumbs which are caused by the above prewatch script.
So what's the conclusion???
Either wait for the author to update it including the scripts, or leave it alone or..... use it if you can tweak it to some extent.