Product review (4 stars): so the practical thickness of the product is really more like 3 1/2 inches
Adequate product but didn't give me the narrow clearance I needed.  Note that the main body of the periscope is only 2" thick, but the two connecting tubes cannot lie flush with the wall and dryer, so the practical thickness of the product is really more like 3 1/2 inches.  That is, your dryer must still sit out about 3 1/2 " from the wall behind it with this periscope.  That's better than the usual flexible vent tube, but still an appreciable thickness.

Also, you can't see from the photo, but the main body of the periscope is rectangular when looked on from either tube side.  If your dryer hole and the hole in the the wall are not lined up horizontally or vertically, you can rotate the vent so it is diagonally placed.  However, you will need clearance to accommodate the square corners of the vent if rotate the vent this way.  This was another problem for me, because the hole in the wall behind my dryer was only 1/2" off the floor, while the dryer hole was 5 1/2" off the floor.  I could slide the periscope to the right distance between the two holes, but couldn't install it because the lower corner of the vent bumped into the floor when rotated to the diagonal angle it needed to reach the other higher hole.

Construction of the product is adequate, but as someone  else has noted, the metal is "beer can" thick, so has to handled with a little care.

This means that if your dryer hole and hole in the wall are not lined up  horizontaly or vertical