Product review (5 stars): Well designed, much better than square one it replaces.
I needed to replace an similar type unit.  It is square and has a square closure flap but I don't recall the name.  This unit is much better in design and more thoroughly thought out as to design and use.  The flap in this unit can be locked in place with the control/set lever shown in photo.  So you can lock it open or closed, a problem with the other unit was the flap would fall between dryer loads and would have to be reset.  Plus this unit came with two nylon closures for the flex lines.

I HIGHLY RECOMMEND IT.