Rehm runs and jumps with a specially designed blade that is 15 inches longer than his other leg
I can't imagine why anyone would accuses him of 'cheating'
The device is like a spring, so it stores energy as well as having extra length and mechanical advantage, and better still its far stronger and requires much more force to break.
I'm sorry he lost his leg, but there is no why this is 'fair' by any sense of the word.
It would be like wearing $500 shoes in a marathon when other runners are barefoot. Or like using a wind tunnel to train your bobsled team!