The fixed blade is considered a concealed weapon because it is ready to use. To be an illegal concealed weapon, two conditions need to be present. The weapon has to be concealed and it has to be ready to use. Since folders are "not ready to use", they are not considered concealed weapons. Likewise with an unloaded gun. In a scuffle with an LEO, a fixed blade can be brought into play quickly with potentially grave consequences to the LEO. LEO's frown upon things that represent a potential theat to them. Folders in a scuffle are difficult to open. Fixed blades are not per se more deadly than a folder, but statistically they are the most common knives that are used in homicides. I had the unfortunate experience of dealing with a case where a young man had his sternum (breast bone) split with a buck knife. Despite all our efforts, the young man did not survive the attack.