Is there any downside to the pulley kit? I mean will it hurt the car in any way? Will it ruin the air conditioning? And don't pulley kits usually make around 6 to 12 hp?

Sorry for being noobish. I would buy it and the Kleeman ECU upgrade and that would be around 23 hp increase which is a good increase. Kleeman have dyno showing that their ECU upgrade will give 13 to 15 hp at the crank.