Product review (3 stars): Installed properly, but can't say that it really helped.
I bought these since my laundry hookup is located on second floor and I already have front load washer/dryer unit, and they were causing vibrations.  These were properly installed per instruction, but it still causes vibrations when the washer is in wash, so I can't say that they really helped much.  They did reduce the vibration slightly, but not what I was hoping for as it sounded too good to be true.