I did a face plant into the back of my buddies bike at maybe only 5 mph. I fractured my wrist and broke some fingers and developed fluid around my heart which is still there. The thing is I have never hit anything so hard in my live and once I was a passenger in a Volkswagen bug that hit a large car head on. I went thru the windshield and hit the other cars windshield and bounced back into the Volkswagen hard enough to break the seat and was lying in the back when it caught fire. The bike accident was worse. I stopped instantly when my face smashed into my buddies bike. Cracked my helmet and shattered the face shield. I can't imagine what my face would have looked like in a half face helmet.  It's your head, and I guess it all depends on how much you value it. I'd go with a full face.