Great for downloading youtube videos but if you only want to download the audio there is a problem that you have to be a PRO youtube user otherwise you get:

"Youtube switched to separate audio/video streaming technology for higher quality formats and no longer provides direct 720p (Since 24 September 2018)/1080p/mp3 streams. Converting these streams to downloadable formats for you needs powerful server infrastructure, therefore 1080p/mp3 downloading has been limited to PRO users".