Product review (2 stars): Great in theory; in practice: not so much
I bought this in order to get a crucial couple of extra inches behind the dryer so it can sit closer to the back wall.  The illustration and design concept suggest it ought to do the trick.  Alas, it turned out that the installation was no more compact than a flexible 4" vent hose.  The problem is that the round vent flanges protrude so much as to negate any space-saving advantage of the flat exhaust duct.  The flange SHOULD be designed so that the flat part of the periscope is snug against or very close to the back of the dryer; it isn't.  If re-designed, this product could serve a real purpose; right now, it's no help.