Works well enough and integrates pretty nicely into youtube.

Sometimes the extension will stop working because youtube changed a few things. When that happens, updates usually seem to arrive within a few days.

I've seen some people complain about this extension not offering video+audio streams in certain resolutions on certain videos, but that's hardly developer's fault (since they just "expose" the download links that youtube player uses. If a stream of certain resolution and/or audio quality is missing, it's because Youtube no longer supports that format of stream).