They will crack, grooved are better for road use as they stop pad glaze. If you do use drilled discs, make sure you clean them out every couple of weeks or even more often, they crack due to heat and cooling cycles, and if the holes are full of brake dust, the discs cool down and the pad dust hardens to the point that as the disc contracts as it cools, it cannot compress the build up of dust in the hole anymore and is forced to crack!