I guess no need of spoiler, but still as a formality I added. My friend has seen the Korean movie as well. Here they have spent a lot of time giving back stories to the main characters, adding some melodrama. He said songs are all trimmed, each song plays about 2 mins, not more. Several shots seen in the trailer was missing (Unless my friend had dozed off in between). So, editing was crisp.
I also asked him specifically about KRK. And he said that his performance was good. Basically he plays a jerk in the movie & since that is even his real life image, it fits him to a T.