Given roughly the same size engine, a brushless motor compared to a nitro would probably produce the same ammount of power in half the size, so yes, they're very powerful. They're also very expensive .

The t-rex is not a very big helicopter. Being hit by the blades would probably leave some nasty bruising and some good cuts, but wouldn't be overly disastrous. Now, I wouldn't want to be hit by anything bigger than a .30 size heli, nitro or electric. THEN you're talkin some serious pain! Either way, it wouldn't be the first time someone has died from flying RC helis. There was a post not even a few days ago just on this subject if it interests you.