I can attest to that thing's utility in OU, even if I had to use a different EV spread than what the site gave. Gliscor, Hippowdon, and Mamoswine become almost non-issues with Mesprit around, and so does DD Gyarados (barring flinchax). Swampert is practically forced to Roar or flee as it can't do much else, especially when running Calm Mind. As for DDMence, Outrage will fail to OHKO Mesprit and it can easily retaliate with Ice Beam. Not to mention it takes physical hits like a champ in general with max HP and Defense EV's and can actually attack back.