good

Can only download 720p it seems but it's also the only add-on I've found that works as intended.

Works, HD formats too.

It work and i recommend it.

Very fast because it's not using a 3rd party converter/download service but you directly pull the video from YT as fast as your internet connection allows you to.
The download button sometimes takes a hot second to appear, which would be a nice fix.

So Far I have had good results with the extension. I'm able to download any video at 1280-720, mp4 or webm format. The speed was impressive at first but slowed down to moderately slow. I doubt the extension is at fault here and I suspect either my ISP (Comcast) or google not sure but I'm giving the author 5 stars.

update: 12.30.2019:

I added an extension called "Magic Actions" it sometimes allows the download button and sometimes not. Now it is showing a two download buttons.

It does what it's supposed to do.
Absolutely love it

Daumen hoch, funktioniert!