first, this extension asks you to upgrade to pro at a fee to start downloading audio streams in 256kbps mp3. secondly, clicking on download as .mp4 forces you to install a native extension that corrupts your windows installation (tested in x64 win10). even after recovering from the corruption and reinstalling with a clean boot, the native extension still forces you on its page when you click on download as .mp4.

all in all, the worst extension i've ever come across. 1click youtube download works far better in all res, hell, even lets you download in 1080p.