It works, but practically only for 720p video. Does the job if you really want a downloader browser extension, but it's really limiting otherwise. I'm not bothered that mp3 is limited to a paid feature, it's easy enough to convert video files to audio only. What does bother me is the lack of 1080p or higher downloads.
Their excuse about needing "powerful server infrastructure" for 1080p+ downloads is a weird one, considering this is all done locally. You could convert to mp3 locally as well, but that's whatever.

All in all, it works. But you're better off just using software that lets you download as you please.