I have two Shoei Neotecs (the full face flip up with the internal retractable sun visor - one black helmet, one white), one Shoei full face flip up (predecessor to the Neotec) without the retractable sun visor, and one Nolan full face flip up with a retractable sun visor like the Neotec. Last September on a warm day, I decided to wear a half helmet on a planned 150 mile ride; the main reason I wore the half helmet is because it looked "badder" than a full face helmet, and secondly because of the warm weather.
Keep in mind I have been riding continuously for over 50 years and hadn't had an accident or even a tip over that was my fault during that entire period.
To make a long story short, I was riding way too fast, went off the road, hit some rocks and ended up being thrown off the bike face down into some large (bigger than a breadbox) rocks. I needed 9 stitches in my right upper lip, my right upper eyelid was split and had to be sewn back together by a plastic surgeon specializing in eye surgery, I shattered all of the bones inside my right eye socket, and broke a few ribs and vertebra. The worst result was that with the shattered bone anchors used by my right eye's controlling muscles, I had double vision for about 5 months while the bones and muscles healed. I am just now getting rid of the double vision. However, my right cheekbone area is still sore and very tender to the touch and the vision in my right eye can no longer be corrected to 20/20. I was very lucky to have not totally lost my right eye.
I will never wear a 1/2 or 3/4 helmet again - NEVER; a full face helmet now goes on BEFORE I ride. None of the facial or eye injuries would have occurred with a full face helmet.