They work fine. I have one. You'll need to do some small modifications to it (like adding a bucket to collect the grain, maybe adding a drill or electric motor to drive it. Hand cranking any mill gets old, fast). Malt/grain conditioning (see Braukaiser's wiki) is highly recommended for this type of mill.
I get efficiencies in the 80s with mine. Look for the "ugly junk" thread on here for the best pictures/instructions.