As it turns out, slots also mean more pad wear. They were designed to cut the pad, providing a fresh contact surface. The surface of the pad can "glaze" (is that the right terminology?) under heavy braking forces, a.k.a. race applications. This would cause a reduction in brake effectiveness. So, cut a new surface, keep friction up, keep good braking. But sure, why not, it looks cool, and pads aren't that expensive or a P.I.T.A. to replace, right? You probably wouldn't even remember that you replaced them 20,000 miles ago, instead of 25,000 miles... As for drilled, it is pretty good for everyday driving. Allows gases built up between rotor and pad to have a place to escape during braking.
I installed EBC's dimppled and slotted, along with EBC redstuff pads.
About 15k miles on them now:
Almost no rust or corrosion on the non pad portion so they still look great. Love that powder coat!!
Little less break dust.
Huge difference in stopping power. The reds are a little hard so you have to warm the up to feel their full power, but wow.
I only wished I had painted the calipers with the caliper paint when I got the car new instead of waiting, they rusted on me through the paint again. I wish I could justify getting new so they're nice looking but meh I'm on a govt salary.