User blog comment:TheCarrotSaysYumYum/FT0 - Game of Truth, Review./@comment-24066070-20140817132729/@comment-7418318-20140818070054

It was only said to force the people within to tell the truth, so it likely wouldn't have helped Ivan. Not saying anything at all is not lying, thus wouldn't be prevented by that item... besides Laxus wasn't lying in the first place, even though Ivan didn't believe that.

Same thing with Erza. She never lied to Kyouka. She was just refusing to answer at all, thus something that prevents lies would have been useless in that interrogation. Besides considering the reprimand and punishment Kyouka got from Mard for playing with a Human and since they already had the chairman working on the problem, I think the possibility of learning Jellal's whereabouts were just an added bonus rather than the real reason for the torture.