Zircon blocks are the most effficient small boat blocks that Harken has ever made. Zircon blocks have industrial ceramic ball bearings mounted inside caged races.  The cages keep the bearings apart so they don't bunch up, touch and stop each other.  The result is a very free-running block with less energy lost to friction.  Give an unloaded Zircon block a strong spin and you will notice it spins for an incredibly long time. Ceramic is a more familiar name for the metal element Zirconium.  Zircon bearings are about 7.5X stronger in compression than stainless steel bearings.  They just don't absorb as much energy before starting to roll. Zircon blocks are expensive.  But this is competitive.  If Harken don't offer this level of performance, someone else might.  Sailors know best.  If you try one and find value, you will buy more.  The opposite is also true.  We're good with that.  
