Product review (4 stars): It has several applications for use.
I got this kit as to redo my dryer vent duck work to the outside.  The kit comes with two plastic 90 degree 4" elbows and about an eight foot length of 4" stretchable aluminum piping.  The elbows screw into the piping.  When stretching the piping to desired length it is best to have two people.  One elbow end has a rubber gasket inside for to snug up on the back of the dryer coupling and the other elbow has the gasket on the outside for connecting to solid 4" vent piping.  Although the connects might be ok, I will wrapped the connections with aluminum/duck tape. I did this for added insurance so that it will not separate and to minimize air/dust/lint seeping out.  Also, what I found to be a good idea, where the elbow connection connects to the dryer piece, I also placed a small 2" x 4" by about 6" long piece of scrap wood on the floor and wall area behind the dryer as to hold it in place better so that it is less likely to separate from there.  All in all, this kit did the trick for me.