well first of all Google doesn't want you downloading videos, that is why you won't find apps that do so in the PLAYstore. IMO this is a bit of a grey area because it is borderline piracy if not actual piracy. That said, Amazon doesn't care if you download Googles videos so IF you are looking for a "more trusted" place to find that kind of app I would look there.
Finally in order to balance out Universal karma you may want to consider doing the following IF you download YouTube Content to your device
- let the video Play from YouTube's site/app [with the sound off] so it still registers as a view. Do this from your Tab or PC etc when it is not otherwise in use.
- Leave a comment about the video on YouTube's page for the video
- DELETE the videos after viewing them
I say this becuase YouTube is branching out into producing Great first run content like the Geek and Sundry Channel
Geek & Sundry - YouTube Programing like this needs to show views and interest to continue to be funded.