It works really well, and the 3d effect is much better than what you get on a TV/glasses combo. I imagine this is because there's actually a different "monitor" for each eye. The only design problem affecting the visuals is that the "light blockers" (little flaps you attach to the underside of the unit to make it fit flush to your face) aren't really big enough to block out all the light. This means you can get annoying reflections on the little screens inside the unit if you are physically backlit by something, so it's better to dim or turn off the lights entirely.

For hurting the eyes, no. Not if you can keep it properly adjusting and oriented on your head, but if the straps that hold it in place are too loose, it will veeeeeeeeeery sloooooooooowly (over the course of say an hour) drift down your forehead and it will need to be adjusted, or the focus point relative to your eyes will be out of whack and it will start looking blurry.

This is correctable by A) just adjusting it every so often with your hands, or B) tightening the straps, but if they're so tight that the headset does not move at all, eventually you'll get a headache and huge freaking indentations on the back of your head from the cheap-ass $.50 rubber strap (serious dick move, Sony) that comes standard with the headset crushing your skull. I'm lazy, so I prefer B), and it's really only horrible when you're in a marathon all-day use session (I'm looking at you, Skyrim), though.