User blog comment:TheCarrotSaysYumYum/FT0 - Game of Truth, Review./@comment-24066070-20140817132729/@comment-24066070-20140818203446

As you said, neither Ivan nor Kyouka believed that Laxus and Erza respectively were telling the truth. With this item, they would've known the interrogation was useless after the first "I don't know", though Kyouka would've probably continued the torture regardless.

If Ivan had this item he could've found a way to use it against Makarov and then he wouldn't have to bother confronting Laxus (from his reactions during the fight he clearly underestimated Laxus' strength, while he likely knew from the start he wouldn't be able to extract the truth from Makarov by force).