It works and will download videos, but it will only download the AVC (MP4) version of videos. For example, YouTube primarily uses VP9 and Opus codecs for their higher quality streams now, but this will not download those versions and will instead download H.264 and AAC versions, meaning they are lower quality as a result. So while it works and downloads YouTube videos, it will not be pulling in the best possible stream despite having selected the resolution I wanted in the video player first.
Very fast because it's not using a 3rd party converter/download service but you directly pull the video from YT as fast as your internet connection allows you to. The download button sometimes takes a hot second to appear, which would be a nice fix.
So Far I have had good results with the extension. I'm able to download any video at 1280-720, mp4 or webm format. The speed was impressive at first but slowed down to moderately slow. I doubt the extension is at fault here and I suspect either my ISP (Comcast) or google not sure but I'm giving the author 5 stars.
I added an extension called "Magic Actions" it sometimes allows the download button and sometimes not. Now it is showing a two download buttons.