i have the march pullies that are piggy back and they were very easy to install and no vibration. could not tell a diffrence in power but i got them b/c i ran out of bolt on's to buy. it was the last mod i done b/c in my opinion they dont produce much more power and thats the main reason i went with piggy back and also b/c they were cheap
i love my steedas and would say get them. installation isnt very hard but air tools are a must for it or else