They actually dont cause any more damage than woodies as long as you dont tighten the blade grips too tight. I think many guys are overtightening their grips and thats why theyre getting big damage. I tighten my grips just enough so that I can flick the blade with my finger and it will move about an inch.
Overtightening causes the blades to be too rigid and when you hit something, the shock gets transfered right through the whole heli instead of having the blades fold on contact.
Thats just the way I prefer to have it set up.