Product review (2 stars): They sort of work, but...
These brackets are required when stacking the Duets, but they really are a cheap solution.  After awhile the screws will come loose and strip out so then the dryer slides back every time you close the door.  Then you put bigger screws in and it holds tight again for awhile until they work loose again.  Repeat.  I would have gladly spent another $10 for a more secure and lasting solution.  After 5 years of just general frustration with having these things stacked, I've decided to customize our dumb laundry closet sot hat the dryer sits on a shelf instead of directly on top of the washer.  Once you have to move these combined units in and out a few times it gets old quickly.