Yea are suppose to get about 3 or so hp. It also takes that A/C lag feeling away too. Better throttle response as well. Some people say yay and others nay. Do what you want, dun let anyone sway u away from them if you want them. GOOD LUCK!
MLB is right. You get no real gains from the pullies. It's more of a butt dyno feel only. If you can get a set for cheap get them, but don't buy a set b/c it winds up being more of a waste of money. I've got a 2pc set. I love them you do get a little better response , but I bought them off a guy in my town for cheap. The only one you should buy new should be a 4pc set, but they are uber rare from what I've heard.