This is the only add-on that really let's you download YouTube videos, convert them to MP3 and more without ads. Simply works.
And the support is great. Answering in a day.
Update July 2020:
Still the best one :)

Since it wants money....

Really the simplest way of downloading. A button is added to the YouTube website - no messing with your toolbar or cutting and pasting URLs to separate websites.

As an update - you now get a toolbar option. This is due to YouTube constantly changing their interface. This is a nice option - it means you don't have to wait for a plugin update when this happens - you can just use the toolbar icon for the interim time period.

Uma droga, tem que pagar se quiser baixar mp3.

god

Payant...

well

The extension works fine overall, though the free version will only download up to 360p. It would be nice if free would work up to 480p. HD downloads require a donation due to server time required (which I'm not averse to giving, as the extension works well).

4 stars because extension cannot leverage local resources for transcoding, rather requires access to an external server.

Nie można zapisać w formacie MP3, bo ""720p+ downloading has been limited to PRO users"".

wow it's good extension

"720p+ downloading has been limited to PRO users"

Well done Akansas