Only two of these were mildly meaningful (whizzing on a bike, and not adding weight need to be said?) and as others have said, those two aren't so bad anyway. Forearms on the top bars is fine. It gives the hands a rest. It gives the arms a rest. It's more aero. Basically it gives you break. It's best for well known good conditions though and obviously requires caution. Of course you could get clip on aero bars. Top tube descending also ok, although I don't see the point if you aren't a pro.
So was there anything useful in the video? Still I suppose we're entertained.