They have always worked for me and fly very accurately to my field points.
Krojeman, the only way I know that a thunderhead will break is if the blade(s) is not correctly installed in tip correctly or the back band is not properly tighten squarely over each blade. This happen to me before when I tried to insert my blades without my eye glasses on. I have taken an arrow with a thunderhead on it before and shot a junked car door out in the woods and the arrow penetrated half way through the door and the broadhead could still be used for hunting after properly installing new blades. I have had the old bear broadheads curl up on me when hitting the shoulderblade but I havent had any preformance problems with the thunderheads.

Bobby