This is just a helper extension for the website uniDownloader. Although a lot of the formats you are going to really want to download are not even available off of that website and you are going to need to run the UDL Client application to get what you want.

The UDL Client windows application does appear to do what it says it does. Copy a video url into it and it will give you a selection of different resolutions and formats for you to download the video.

Can you really trust this separate free video downloader application? I don't know. It's a closed source program. Could it hide some hidden playload? Maybe? The UDL Client does appear to download videos (I've only used it with YouTube.) in whatever resolution you want for free; unlike most other video downloader extensions that require a paid version to get all resolutions.

I wouldn't blame you if you didn't trust their UDL Client. It does seem to good to be true. Although, it does seem to be doing what it advertises. I can't tell you if it isn't also doing something nefarious behind the scenes also. But it does seem to do what I want it to do so far.