The biggest disadvantage to over speeding, is the unnecessary fatigue on the airframe and other components on the helicopter. I have done them at IRCHA and other events, during our team`s demo hour, but I don`t make a habit of it. It`s just too hard on the helicopter. I watched Duncan do an over speed at the Olando Helicopter Blowout in 2015, that was so violent that it bent the main blade bolts on his X7. They had to cut the blades off, to get the bolts our of the grips.