Having only done Kukki style sparring, I can't properly compare the two but I can say that Kukki style sparring emphasises the athletic ability of the practitioner over realism. I have always found this strange. This method of sparring is lots of fun, is good exercise and requires a lot of skill but doesn't even remotely resemble the core of the martial art.

I believe that this style of sparring arose as a result of the equipment used (heavy torso padding) and the no punch to the face rule. It's impractical to block a kick to the head because you'll just hurt your arms in most cases and there's no point blocking your torso because the padding will do the job for you. The logical consequence is that arms are basically momentum generators, instead of used in any practical sense for defence. The purpose is less to block your opponents hits but to accept that they'll land a few blows and try to score more points than they did. This is only possible because kicks against the torso guard don't hurt much and can basically be ignored (barring the occasional powerful back kick).

I have always thought that this form of sparring encourages sloppy technique at the expense of power and speed. You are only able to generate that much power quickly because you can afford not to guard yourself with your hands. In a situation where you are not wearing the torso guard, those kinds of kicks open you up for major damage.
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Self Defense
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