The app is great, but wasn't google recently banning user accounts for it? Youtube account and google account is same thing, so this app is useful only for othwerwise ungoogled users
Like all third-party youtube apps and downloaders, you should use a dummy account that's subscribed to all the same channels as your real one.
I suppose and app like this could provide a third party (self host able api) account service - recording history and managing/syncing playlists? Maybe with an option to merge in entries from Google account playlists from time to time?
Playlists are nice not just for playing/listening, but also downloading for offline use/backup/archive.
Ed: i see that it has local history and playlists, with option to export data - but apparently no option to load data (whether from youtube/Google or an earlier export).