Product review (1 stars): IT'S NOT ASSEMBLED CORRECTLY, THE BLADE IS INVERTED (and a washer is in there too) such that the blade never touches the grille!
Warning:  this part does not function when assembled as in the picture.  In fact, complaints in these reviews stating that the chopper doesn't actually chop are correct, when the item is incorrectly assembled as shown in the photo.  For the part to actually work, the blades need to contact the holey grille surface.  As shown, it is clear that the blades do not contact the surface.  I have supplied a clearer picture herewith: notice that the blades hover ABOVE the grille, not touching it at all.  (And no, the spring can't pull it closer when it's fully installed in the dishwasher.)  I have contacted Amazon about the incorrect assemblage and they have promised to contact the manufacturer.  For the truly industrious and fearless but impatient folks out there, it is possible to correct the part yourself.  In short, here's how:  carefully but forcefully pry open the four flutes of the locking 'nut' in such a way that the plastic shaft end is not substantially marred.  I did this using a very stiff but very narrow knife blade, being quite careful not to cut or stab myself.  Gloves would be good.  Remove the 4-fluted 'nut', remove the blade, remove the washer.  Flip the blade and reinstall on the shaft.  Next add the washer.  Restore the 4-fluted 'nut' to original shape by bending the flutes back to their original positions.  Force the 4-fluted 'nut' back onto the shaft.  Voila!  Observe that the blade now contacts the holey grille surface as designed.  Clearly, the chopper CANNOT chop without contacting the surface.  If not chopping, the holes fill rapidly with food particles and water flow through the assembly becomes insufficient to clean dishes.  Don't buy a new dishwasher, get the right part.  Question: did Whirlpool do this on purpose, or by accident?  I hope Amazon will let me know the answer to that question when the investigation is finished.  One star because the part doesn't work, but looks like it will, and costs $15.25 while secretly killing your dishwasher.  Now that's a serious pain in the hindside!