@MaxfinitoOh no, let me guess, you also think that Ninjas were black clad shadows and not just guys usually dressinf up as a servant or farmer, stabbing their targets once getting a bit to close like a psychotic maniac in prison with a toothbrush shiv and run away.
The reason its not in use is that trying to run with it in 20-40KG in gear will * up your back, easily makes you stumble and harder to react to anything. Its stupid going into a fight like that, not to mention you literally put your most important, and usually least armored part of your body, the head literally first.
If that works, why doesn't the japanese military utilise it?