Product review (5 stars): Needed, bought, LOVE THEM
We have a stacked Duet unit in a 100 year old frame house in Chicago and had been using standard HVAC vibration pads to minimize the wicked vibration during certain spin RPMs of the washing machine.  The whole second floor would shimmy during use.  AFTER installing these, it has been reduced by a SIGNIFICANT amount to the point where you have to be near it to even feel it.  HIGHLY RECOMMENDED, worth every penny.