Product review (5 stars): Actually works
Short answer:
We bought these several months ago, and they really do help.
We are on the 3rd floor of an apartment complex and it has reduced the sound and vibrations considerably.
If you are considering buying them, get a set.

Back story:
We came from a house that had a slab foundation (just a big block of concrete underneath the whole house), and the washing machine sat on the ground floor of that house. We have a front load, high capacity washer, and we never knew there could be a vibration/sound/movement problem in our old house on that slab foundation. The machine just worked all day with no issues.
When we moved into the 3rd floor apartment, we noticed the change right away. The washer was sooo much louder and it would even "walk" a bit. It wouldn't walk far because it would stop against the left wall and just remain askew there. So, we bought these rubber feet and put them underneath the washer.

I won't say the sound and vibrations have completely stopped, because that is impossible when you have a front load high capacity washing machine on anything other than a slab of concrete. BUT, it has definitely stopped the walking, and definitely reduced the sound.

We even had a washing machine tech come in afterward to make sure there wasn't anything wrong with the machine, and he said it is completely normal. Being on a higher floor will still cause that sound and vibration, so the drum and everything else in the machine are actually still fine.