Downloads videos yes, but it's also very intrusive. It invades the graphical interface of Youtube with not only the button, but also a big message about a premium product when I tried to download an MP3. I could not remove the message until I uninstalled this. Bad decision on your part.

The very intrusive message is:
PRO UPGRADE : Since Youtube no longer provides direct download links for 1080p and MP3 qualities these two qualities require server infrastructure for processing, therefore user needs to Pay and Upgrade here >>>, you have the choice to pay whatever you want for this one-time upgrade which helps me keep this service alive for all users.