ViDL for Mac is basically a nice UI in front of ViDL (youtube-dl). I use it to download Twitch videos when the videos are only for subscribers. First time you try it it'll ask for your Twitch user and password (actually launches a Webkit page to show login screen) and after that it'll automatically use it (so it's not for circumventing security, you actually have to be subscribed to the channel).

Pretty simple to use. Copy the URL, click on Find, then select the one entry and Download. It downloads the highest quality version it finds and you can't even set the destination file name. It does the "download thousands of little chunks and merge them into a final file" which all ffmpeg downloaders do.

I still use 4K when I can because you can choose which video quality to download (or even just audio if available). You can set destination file name and it downloads as one continuous connection. But when I need to login I use ViDL and it works fine. Mind you 4k Video Downloader is not free so if I did it over again I'd only use ViDL.