Product review (5 stars): Easier than using an elbow
If you need this, then you need it and it works perfectly.  Easier than using an elbow.  The lower portion is fairly strong so you can put some wood in back of it so it doesn't push back into the stud bay after you put the wall board up making it difficult to attach the dryer hose.  Such might not be needed depending on the depth of the stud bay.  Use this with the two piece dryer dock sold here on Amazon.