The Cold Steel Urban Pal punch dagger is one of a number of new and questionable knife designs targeted for the urban self defense market. Its one and a half inch blade, even with the serrated edge, is not enough to be an effective visible threat. Legally it’s uncertain–the overall length may fall within local guidelines, depending on your area, but the design itself may classify it as a weapon rather than a pocket knife. Always check your local laws first.
The modern punch dagger design dates back to the days of the ninja, when fist load weapons were sometimes devised on the spot. In an expert’s hands this sort of device, even if made from wood, can be deadly. In an amateur’s hands, perhaps not, but the use of such a knife is more intuitive than most. The common mistake a knife fighter makes is a downward stab, easy to deflect and avoid; the instinctive use of a punch dagger is a straight punch, the same as a fist. If you hit, even with a glancing blow, you’ll do some damage. That might make an attacker run away, or it might make them really really mad. People often don’t even notice stab wounds until much later, when the fight is over.
The legal risk involved with such a knife makes its real self defense value questionable, as there are many perfectly legal and common items that can cause as much damage with very little training, and not land you in court.