Product review (5 stars): Pleasantly surprised
Disclaimer first, I actually purchased this item at a local Home Depot.

I have an LG front-loading washing machine.  It is great except, you guessed it, the incredible vibrations during spin cycle.  I have a laundry room on the first level between the kitchen and the garage, but the laundry room also sits atop of my basement, so there is not concrete floor underneath it, just a vinyl (i.e. flexible) flooring, subfloor and then open space underneath.  Pretty much the worst flooring you can have for high speed washers.  When the washer spins up, it sounds like there is a helicopter hovering overhead and you can feel the vibration on the other side of the kitchen through the floor. When I started researching this problem, I was VERY skeptical of the various pads available.  But it was either this, or moving the machines to a different location and installing new plumbing.  I also read people have success by putting down 3/4" plywood underneath the washer, but that's a tacky look I would rather avoid.

The pads are rubber with a hardness somewhere between car tires and a hockey puck.  Installing the pads was a breeze: lift up one side, slide the pad in, align and drop back down; repeat 3 more times. There is a circular recess cut into the top of each pad for aligning with the feet of your washer and grooves on the opposite side for gripping the floor. Once installed, I put in a load of laundry to test and amazingly enough, they worked!  The washer itself still vibrates quite a bit, but the pads somehow absorb most of the vibrations and keep them from being transfer to the floor.  I could not feel any vibrations if I stand more than a few feet away from the washer, and this is a huge improvement for me.  I end up buying a second set to even the heights of washer/dryer.

Anyway, money well spent for me.  I can't speak for everyone's situation, but if you have similar flooring as mine, give it a shot and see what they can do for you.