It is a shame that this is not more popular. The main series did well, but this one has not seen as much attention. I would say the main selling point of this manga is the characters. In the beginning the characters seem a bit cliche, but as the story progresses and more about their past turns up and see how friends turn enemy or vice versa. It is fun seeing how they develop as the story progresses. Do not expect anything on par or better then the main series, but it is not a super long manga and it is fun to read!