The add-on and companion application function perfectly for me, no download limits like the video downloader I use, bug free, its ad free which I didn't expect to see and it doesn't redirect to a website like y2mate or some derivative to download the video. The quality of the video is based on the selected quality that is playing in YouTube so change it to something like 360p/720p maybe if you are saving on HDD/SSD space. It also registers some memes I get on Discord for download too funnily enough.
The only thing I could nitpick is the file format it comes out in on YouTube is .mkv which is a small price to pay for free video downloading as all you need is VLC player or an online file converter to .mp4 or .mp3 if you really need that and you are set. An internal converter for output to mp4/mp3 would be the icing on the cake but as far as I'm concerned this suits my needs well enough.