Seems really cool but it doesn't look open source, there's any security guarantees within the app? I'm really paranoid of where a put my Google account credentials

I'm pretty sure it's modded version of the official youtube app so no guarantees (Just use a dummy account?).

I'm actually very interested in how the vanced developer has made this. This app is pretty much identical to the youtube app with premium features enabled and ad/sponsor bocking/skipping.

I never log into YT on any device. I still get great recommendations and easily stay on top of my favorite channels. IMO the only benefit to logging in is being able to comment.

--and access to my viewing history and ability to add easily a video to my "watch later" list.

I use a second account just for it

they're free to steal it if they want