Drilled rotors do indeed have a tendency to crack around the holes however EBC hve an answer to this in their 'Spotties', which are not drilled but in fact have blind holes cast into the friction surface. Since the purpose of the hole is to vent away gasses generated when applying the brakes this has a near identical effect to the full drilled solution.

Slotted discs do much the same but are extremely noisy under heavy braking with a speed determined whirring noise.

Unless you are looking for a 'cool' look, do a lot of high speed hard driving or tow a heavy trailer a lot I wouldn't bother.....