A Barely Adequate Solution
As I was about to have my third vitrectomy we decided to buy the head down appliance instead of renting.  It worked ok but the knurled screws that hold the head cushion at the proper level continually allowed the position to slip despite no matter how much torque was applied.  This is the primary function of the appliance.  We bought the package that included the mirror and fleece cover.  The mirror was fine but the cover was so baggy that it obstructed the view through the head cushion.  It got the job done but easily could have been much better.
Rating: 4 stars