The only down thing might be, that we don't know, if those guys wanted to double cross that bastard, take his money and sell him out to the guards. Though the chance for that are slim. Let's see. They wanted to harm another person for no good reason, they have been a danger, they knew about his ability (MC should be more concerned about the knowledge about his ability to leak out.), the authorities don't seem to be trustworthy as they work for his nemesis. He could have handled this differently and sell them out to the guards, as a concerned adventurer, and if that wouldn't work he can still kill them and the guards involved. I like though that he let the monsters do the dirty work. I was concerned he'd leave traces all over them. (Poison traces or dagger wounds.)