Product review (4 stars): They work.  They really work!
I was sceptical, but I couldn't see paying over $200 for the "top of the line" solution.  I read all the reviews, and some were really good, and some not so good.  But, these were priced reasonably and I gave them a try.
Installation does only take a couple of minutes.  I ran a normal load of clothes, and instead of turning down the spin cycle one notch like we always do, I let it run at "High" (one setting from the fastest spin cycle).  When it kicked into full spin speed, I went from the second level where the washer is to the first floor where my 50 gal aquarium usually rattles and sloshes like crazy on Medium.
How did they work?  Great, but not fantastic.  I still felt vibration in the hardwood floor, but nowhere near what it had been at one speed slower!  No sloshing in the tank at all...
Overall, if others get the same improvement I got, I'd tell them not to hesitate and buy a set today!  Besides, with Amazon's great return policy, if you don't like them, just return them.  (But you won't want to return them...)