Nice to see a Chikara and Yen manga that isn't about how those children deserved it. It's interesting getting one of these from the perspective of the moral paragon character who doesn't agree with the extremist vigilante's methods, but cannot deny that things would've been worse had they not acted at all. De-centering Sengoku from the protagonist slot lets us see someone like Aizawa or Sakurai from the perspective of the people around them.
I think, compared to the usual "and then they got away with all the wild shit they did for the last thirty chapters" ending, having Sengoku willingly accept a prison sentence is ultimately more satisfying. He believes in justice, principles and accountability, that there are things one should and shouldn't do, and killing someone in cold blood, no matter how reprehensible they might be, is something to which society absolutely shouldn't turn a blind eye. Sengoku said it himself: he did something to help the world, the best thing he's ever done, but that something was tasing a man, tying him to a tree and stabbing him to death, and if a principled society doesn't want someone like that walking the street (although, last I checked, over 90% of all criminal trials in Japan end in conviction for the defendant, and that number is closer to 95% for murder trials, and numbers like that do not occur without some kind of collusion and corruption), standing by his justice means accepting that judgment.