If you're talking about the German ones, yes, they are very good. I had one on my Gran Canyon and it reduced the pull a fair amount. Nicely made, excellent machining and finishing. Hard to beat for $80 or so.
I have a Evoluzione Clutch Slave. I would say they are one of the most popular upgrades. Yes it will decrease the clutch pull, or as some say get some man hands, you girlie man. If you ride hard enough you dont need a clutch, just speed shift it....j/k! I got mine since the my OEM was leaking. I didnt buy it for lighter clutch pull. I have seen them on EBAY or get one directly from Ken at http://www.evoluzione.net/