I have been using this addon for years, and i've NEVER had issues with it other than that sometimes an adblocker needs to be adjusted so my download request isn't blocked. But that's an easy fix.

Super easy to use, downloads in a variety of formats, and the costumer service have always been super fast to reply and very helpful with troubleshooting (i really should know by now that whenever it won't download, it's the adblocker messing things up:p)

Best youtube downloader out there! I always recommend it to people who are looking for a downloader :D