Product review (4 stars): These work pretty well
I have a laundry room that sits on the main floor, but over a basement. Every time I'd run the washer, it'd sound like an earthquake was rumbling through the house as it went past a certain speed in its spin cycle, and inevitably, it'd be a few inches off of where I thought it was. These things mostly fixed the problem. When I ran the washer empty, it didn't move at all. With clothes added, it still made a bit of a racket (I think due to the drawer underneath it not closing completely), but at least it didn't visibly shake as much, and definitely didn't walk like it used to.

On the other hand, I didn't have high expectations, as I figured if these things worked, the manufacturers would just include them. Amazon's high ratings for the products convinced me to give them a try. I think they were worth it!