It works, but I unpacked the XPI, (just convert it to a zip in your extensions folder if you want to see for yourself) and the code just seemed generally suspicious at a glance,(it also requires access to all sites???) so I got rid of it. If you want a working addon, check this git.
github.com/EltonChou/TwitterMediaHarvest/releases

require access to ALL sites, instead of X Twitter websites! a spyware behavior!

I was first sketchy about this downloader, but it works, simple ui, and just downloads videos from X with no problems

Works out of the box

Doesnt work.

the least worst of all the extensions seen on the subject

Yes