I wanted a simple downloader compatible with DASH that did not rely on 3rd party websites and/or PRO payments to do its work. I already had FFmpeg, so this was fairly easy for me to set up. Once set up, in two clicks I can get correctly muxed DASH videos in my download folder. Maybe if you don't know what nodeJS or FFmpeg are it sounds scary to install? Firefox runs a batch file, the batch file executes nodeJS, which executes FFmpeg.

A download button in the YouTube player page would have been preferable(but susceptible to Google messing up the layout), but the standard addon button isn't terrible.