I have brewed with this a few times and like the results from it. Unfortunately I am going all Electric and it will not work with my current setup so I have to part with it. I paid $60 for this last fall with my setup and will sell it for $40.
http://www.blichmannengineering.com/hopblocker/hopblocker.html
http://www.blichmannengineering.com/hopblocker/hopblocker.html