Lenticular 4D light field display don't cause focusing problems, so no headache! This is now, not in the future! This is how ALL the steroscoppic displays should be done! Finally it has arrived!
Because its so small the possible positions of your head is small. On a larger screen you need to be looking at a 90 degree angle and at a set distance. The further your deviate outside of that spot the less of a depth effect you get. "Glass's free" 3D is just an optical illusion.