I also believe some scenes are faked - at 1:30 the chainsaw is turned sideways instantly, a maneuver which should not be possible with the gimbal setup they are using, and especially not without moving the center of mass way of balance.

Fun video nonetheless! :)

EDIT: Although, at 1:54 the rest of the copter can be seen after the cutting. Strange that they would not include any outside view of the cutting or even the chainsaw in a sideways position though.