Surely there would be some better implementations than this? Those with adjustable or angled grills, one push open/close etc? But I can't seem to find any (at least not for consumers/diy)
Closest ones I could find are:
RED15/20 Round Egg Crate Ceiling Diffuser 150dia c/w damper - not much details and pictures not well labeled, I wonder if the damper works as a shut off valve. Still the air would go straight down.