History is written by the victors - Sefer Milchamot Hashem
Firstly, how pious the Karaite is. He is not a rebel or a mocker. He truly believes that he is in possession of the truth, and the Rabbanites are heretics. He is trying to show them the error of their ways.
Secondly, how his arguments are not very different from those voiced on many j-blogs today. (Not necessarily by the bloggers themselves)
Thirdly, how the Karaites basically disappeared from the radar of the Jewish world.