What identifies Kuk Sool is its breadth. Kuk Sool Kwan is itself a survey of the philosophies and elements which have motivated all of the above mentioned arts. This was intentional -- as a martial art for royal bodyguards, it served as the anti-martial-art martial art, and so practitioners had to be familiar with the techniques of all fighting systems. In its later, post-Korean-War form, as an attempt to preserve all of the native fighting arts of a single nation under one umbrella, this was even more the case. This means that Kuk Sool, on account of its history, is therefore one of the first "mixed" martial arts.
One aspect that makes Kuk Sool stand out is its maintaining of the standards and traditions of ancient martial arts. In an age where martial arts in America have degenerated to becoming mere sporting spectacle on the one extreme or glorified aerobics on the other, Kuk Sool still contains the hallmarks that once defined the true value of martial arts: self-discipline, respect, courtesy, and honor -- all without sacrificing practicality or effectiveness in self defense, but rather enhancing and confirming those purposes through the development of character, inner strength and willpower.
Aside from the fact that no extraordinary skills or abilities are developed beyond fitness, speed, and timing, the drawbacks of MMA are first that it's a ring sport, so its methods are directed against a single individual in a controlled environment. Second, although an athlete with a true Jujitsu background can be an exemplary ground-fighter, MMA's understanding of the art of standup is woefully underdeveloped. This is because it still takes largely from Muay Thai, a poor choice for standup even in its own country, where it is easily surpassed by the superior Muay Boran. Unlike Muay Boran, which was meant for warfare, Muay Thai was meant to entertain an audience and demonstrate the masculinity of its contestants, so it does not focus on fast and expedient finishing of opponents. Concepts like flow, angle, position, or even simple side kicking is absent from Muay Thai as it is usually seen.
The first several belts of Kuk Sool Kwan training cover good, sound kickboxing, as might be taught to a military. These ranks are meant to bring a student up to par with any popularly trained opponent. From there, concepts of position, flow, balance, and defense are introduced which confound standard strength based attacks, and grant a major advantage to a Kuk Sool trained combatant. To gain proficiency in these higher concepts takes many more years than the relatively quick accomplishments of strong punching and kicking, which Kuk Sool also takes care of early on, but the eventual result is undeniable.
Krav Maga is a system that was put together by émigré and Third Reich refugee Imi Lichtenfeld, a renowned streetfighter. It has famously been used to train Israeli police and military. Both Kuk Sool and Krav Maga have in common the fact that they are used as a means of teaching military. A difference between them, however, is that Krav Maga was intended as a "simple, quickly and easily learned" system, and it is used for just that -- that is, to instill a sense of "basic" fighting ability and response to aggression, with moves that "don't require a lot of skill." In other words, Krav Maga's effectiveness is as a short training program that can turn a large group of "cadets" into reasonably capable soldiers, policemen, etc. For the individual who seeks his full potential, however, this is exactly its limitation. By design, it does not teach or incorporate sophisticated fighting concepts.
Kuk Sool, by contrast, takes a long term approach. A more complete system of training for every aspect of the individual is offered in order to create a masterful fighter because it has created a masterful athlete and human being. A foundation laid by correcting body position and strategy away from "crazed instinct" and toward a more efficient aggression allows for immediate practicability in self defense as well as for laying the groundwork for development of more sophisticated skill later on. This is not ideal for rank and file military, and so Kuk Sool is instead intended for special forces, bodyguards, and individuals who want extraordinary, and not merely "adequate" skills.
Although both Kuk Sool Kwan and BJJ come from jujutsu, and although Kuk Sool Kwan trains extensively in ground fighting, BJJ offers more experience in ground fighting because of their exclusive emphasis. Brazilian Jiu Jitsu excels in the arena of one-on-one match fights that adhere to certain rules, because a competitor can tangle with a single opponent and concentrate on the complex chess match between them. This can be of great interest for a lot of people.
The concern and approach of Kuk Sool Kwan, as a bodyguard or special forces martial art, is to include ground fighting but to focus not only on it but also a lot of other approaches to combat. Again, as both of the arts come from jujutsu, the same locks, techniques, and methods of ground fighting are used by each. The self-defense aspect of Kuk Sool Kwan, however, encourages us to try to avoid ground fighting when we can because grappling on the floor with a single opponent leaves one vulnerable to allies of that opponent. Also, ground fighting on gravel or broken glass can be unwise, and some of the common positions used in Brazilian Jiu Jitsu sport competition can leave important areas like the eyes and groin vulnerable in real life situations.
Although Taekwondo and Kuk Sool Kwan both hail from Korea, the nature of their practice and the sources of their origins are quite different. To begin with, while Kuk Sool is a comprehensive art with many different ways of training and many different skills to train, the current form of Taekwondo focuses on kicking to the exclusion of much else, and here mostly the type of kicking that relates to the sport sparring Taekwondo is now in the Olympics for. While some Taekwondo schools will offer "extra" training in joint locks or weapons, these techniques are vastly underdeveloped in Taekwondo, and often represent the instructor's experiences at various seminars rather than being an actual, foundational part of the art. This is because Taekwondo comes from the Korean Karate that the Japanese occupiers brought to Korea between 1910-1945, and is not truly a native Korean martial art, nor an art which had a compelling reason for breadth of training, as, for example, an art meant for bodyguard training would have. Aside from the sole emphasis on kicking, a comparison of Kuk Sool with Taekwondo will also reveal a difference in basic philosophy -- Taekwondo is a purely "hard" martial art, with linear, tense movements, while Kuk Sool looks for circular movements to efficiently redirect where possible. With that said, however, many Taekwondo trained martial artists come to Kuk Sool for the greater depth of training which still maintains some of the basic skills they developed in Taekwondo training. Many Taekwondo black belts who train Kuk Sool think of it as a good "graduate level" program in Korean martial arts.