Both military and specialized intelligence covert operators can't always carry and depend on the full size weapons appropriate in different environments and applications. Additionally, those who can most always find themselves in serious need of a lethal and extremely low profile defensive weapon which can be hidden and most always missed in a cursory patdown. In short, an edged weapon which can deliver a powerful and deadly single strike and still fit completely in the palm of one's hand.
During conversations with those who operate in this manner both domestic and abroad, we've discovered the requirements they place on such weapons and the primary factors are always quality, razor sharp edge and the ability to implement at lightening speed. That being said, the umbrella factor of super concealibility has to be the overriding criteria.
Just like folding knives, you'll likely find small 'hideout' knives that fit the size requirements at many fleamarkets though the quality is questionable at best. The low grade of steel many of these knives are made of eliminates any reassurances of a razorsharp esge that will remain that way and be impervious to the unmerciful environments many of these professionals involved find themselves in. So, where do they go to get exactly what they need?
On a civilian level, law abiding citizens find themselves in 'at risk' situations now more than ever. We sometimes find ourselves in apparel incapable of hiding even a decent sized boot knife or a small folder. Than what?