It works 50% of the times, because the download button appears and disappears over time. I don't know if it is Youtube that blocks the app, but it needs to be updated more often by the author. When it works, it works well, by the way.
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.
When I click to download, it only gives me a file with the name of the video but without any content. For example, I click to download a video of cats, it is finished downloading, I check it and it says 0kb, I open it and it says that the format that was damaged or was changed. In a few words, download an empty file.