Slapjacks,blackjacks, saps etc are extremely effective, if they werent illegal in most places. Similar to a kobuton, you will have to train and use it effectively, but it does pack a whollop. It take percise strikes. I wouldnt take it into a knife fight though. Better off with a stick lol
Also make sure that it is filled with a dense enough material. You want it heavy. Leadshot, powdered lead, tungsten etc.