Hal indeed had no interest in the Nexus stone and even if he ever wanted to see it found or used, it was only out of curiosity to see how effective or useful it could possibly be with him already having his influence spreading with his Devil seed.
He was willing to bet that the influence of the Nexus stone was in no way greater than that of his Devil seed but he also wondered if the wielder of the Nexus stone could discover what he was doing with his Devil seed.
Would the Nexus stone grant them an amazing sensory advantage and sensory attachment to the landmass that was the Haron continent and reveal to them that he had his Seed planted and was already spreading his Devilish influence.
He was curious...
While he did not look like it, Hal was still very much invested in this search of Tanya's.