The Xodus Ultra 4 is what you put on when the run is measured in hours. PWRRUN PB foam gives it a soft, springy 37 mm heel with a 6 mm drop, and an aggressive Vibram MegaGrip outsole keeps that softness attached to the ground on rock and wet dirt. At about 289 g it is a substantial shoe, and it is meant to be.
It suits you on long mountain days and ultra distances, where the thing that ends your race is accumulated pounding rather than pace.
It is not agile. The stack that saves your legs at hour four blunts the ground feel you want on tight technical singletrack, and there is no rock guard, so sharp stones still register. For shorter, faster trail runs a lower shoe will serve you better.