As a twintail Shinja, I sped-read through it before when it came out at the bookstore (which was a pretty long time ago). It's basically GB comedy. Honestly, not my cup of tea at all.
It's really for people with Both GB+Twintail fetishes and have a really crappy plot (I rather read IS with its 3-time repeated developments
). Of course, I once said that plot quality and entertainment value are two separate matters, so to each his/her own