All of those apps use the built-in accounts feature and do not require your information. It's kinda the whole point.The same could be said when you log in to use Google play, Google music, maps, YouTube etc.. Why are you surprised when you have known they ask you to login into their apps.
Edit: I will update the app from time to time or whenever the dev updates it himself. I will provide an updated link as well.
I prefer arktube personally has one issue with dialogs not always popping up on nougat but otherwise is a great YouTube downloader
YouTube Downloader >> http://sourceforge.net/projects/ytdownloader/