Dear God. That's amazing and deeply troubling at the same time. I don't care how good you are, that was hugely dangerous with the size heli. Mechanical failure happens. Radio signals do unexpected things inside buildings like that. Unexpected bird flys down and gets hit. The piros on the ground when the tail caught up a little bit and started bouncing before he got it off the deck... Tail blade catches, boom. Inside parts will ricochet. Way too much can go wrong, independent of skill of the pilot or pilot error.
I love to see the skill involved with a flight like this. But it is also an example of what not to do.
Paul "The Killjoy"