Product review (5 stars): Works Perfectly!
Night and day difference.  The hard plastic top of these feet distributes the load well, and when the washer is vibrating you can feel the rubber layer deflecting to dampen the motion.  In addition to reducing the noise transmitted to the floor, they also absorb enough energy that the washer itself doesn't move as much.  Now my washer hits higher spin speeds too.

Previously used vibration pads from Good Vibrations, Inc. (GVI), which are good at preventing walking, but are bad at preventing vibration (the washer vibrated so bad that it was hitting the dryer).

My subfloor is supported by 4' OC beams, and the washer is in the middle of a span so it wants to vibrate very badly.  But these pads don't let it!  Thanks to Silent Feet!

PS:  Although the "anti-walk" silent feet are a little harder to install, I'd recommend them for peace-of-mind if you have a seriously vibrating washer.