From the reasearch that I have done, the ZPI pulley is like .3 pounds lighter or something.....They basically do the same thing. In theory, however, the ZPI pulley would make a better "gain". I have the Perrin pulley myself - and I'll tell you what, ANY aftermarket lightened crank pulley is better than stock.
As for install, use scionlife's tech article. The hardest part is the lower alternator bolt.
The ZPI pulley's are very good.. they are just slightly lighter then the rest.. No matter which lightened pulley you go with, they well all help with faster revs.. It usually comes down to which pulley is cheaper, readily available and which brand you like..