I've been playing with Ashway 17 Crossfire for 8 years in a Black Prince O3 and never experienced any arm problems from the stiffness.
I'm a 5.0 player and pretty much have good strokes(form that is
) with not to many bad habits.
But, I'm sure this string could lead to arm issues for a lot of people. It's not forgiving but it gives tremendous spin and power as well as control. When the ball comes off the racquet its a "heavy ball" which penetrates the court.
Love Kevlar....hoping when I get older my arm doesn't fall off..