I have had my Kitchen Aid Professional HD since 1998, and use it once or twice every single day at our sporting camp.  I never had to replace the flat beater until it got washed in the dishwasher by accident.  The directions stated to wash by hand which I always did, but a helper put it in the dishwasher once and that caused the black residue mentioned in the other comments.  It is worth having this non-coated paddle, and just washing by hand.