Product review (2 stars): Good Idea - Maybe Not the Best Application
Purchased the Whirlpool 0-18 Inch Vent Periscope at Home Depot to provide more room behind the dryer and move it closer to the wall. The connection from the vent collar to the dryer was not a tight fit. While trying to make an adjustment, the collar separated from the vent. I bought a connector and placed it between dryer output and vent and using a rivet gun reattached the collar. I also applied aluminum foil tape to all seams.  An engineering friend offered his opinion:  The design may help put the dryer closer to the wall, but it is terrible for efficient air flow due to the hard 90 turns. Wouldnt be surprised if the reduced flow impacted the drying time and your electric bill. The most efficient is hard pipe with swept elbows.  Another reviewer was highly apprehensive with amount of heat the vent retained. After purchasing the vent ($20), aluminum foil  tape ($7.47) , 2 connectors ($12) , and vent clamps($4), I did not feel comfortable using this product.