Youtube Video Downloader is an outstanding extension for 2 reasons:
(1) it provides an important functionality and it does it very well. Providing actual video files from YT is not a trivial convenience, it helps me do my work (I am a researcher and physician)
(2) the extension is very difficult to maintain, because of the incessant changes on the YT platform. That is why I strongly recommend everyone financially support this extension who can afford to do so.