Product review (4 stars): Overpriced, but good
Product fit perfect and was easy to install.  The kit is necessary to safely stack your washer & drier, but was way overpriced for what you get in the box.  Four 3-foot strips of foam with a sticky strip, two tiny brackets, and 4 sheet metal screws is what you get.  Whirlpool must think it's worth $20 - $30 just to have the option to stack them.  Overall, I guess it was worth the $20 to gain 10 SF of floor space.  Keep in mind that you may need longer hoses, drier duct, or a closer gas or electric outlet if you previously had the washer and drier side by side.  My wife is on the short side and I would guess the drier would be too high for her if one of those optional storage drawer risers were under the washer.